This is not necessarily a ranking of how powerful a spell is, but how likely I am to use these spells in a game. It's also a little odd, because I'm treating different types of spells differently. For example, global enchantments are generally only cast once, but I may give a global enchantment a 3 or 4, meaning that if I get the spell I am very likely to cast it. However for stuff like combat spells, its more about how often I use that spell in combat during a game.
There are some spells, like Disjunction, that are obviously very situational, but can be critically important when needed. This doesn't do a good job of reflecting that type of value.
Clearly, Life and Sorcery have the strongest overall suite of Common spells. Almost everything you get from them is quite useful. I know a lot of people don't like Nagas, but I use them a lot and think they are worth it. Usually only 1 or 3 units a game, but they are quite potent at taking neutral towns in the early game, which is what I use them for. Chaos has the fewest useful spells, but ironically Chaos still has a very strong opening because the few good spells it has are so good that they make up for the fact that most of the other spells suck.
I'd say that Chaos in general is a sort of odd duck, in that it has a lot of spells that just aren't that good, but by the same token, it has a few standout spells that are extremely effective. It's also a bit strange because I'd say that overall Chaos has the best Conjuration game, even though most of its summons are lackluster. It really rides on Hell Hounds and Chimera, and even Chimera aren't that great. But, what makes Chaos good is the synergy of Chaos Channels, Warp Reality, and Chaos Surge. The hit and miss nature of Chaos also makes it more reliant than most on using all 10 books or at least 9 books to ensure that you get the critical spells. Honestly, masses of Hell Hounds and Chimera when combined with Warp Reality and Chaos Surge are extremely effective, especially when you throw in Chaos Channeled Paladins, Elven Lords, Golems, Barbarians or Draconians. It makes for a very interesting buildup, because the later spells actually boost the effectiveness of units you have been accumulating throughout the game and give "new life" to old units.
I know a lot of people like the many Global Enchantments of Chaos, but really all that matters IMO is Chaos Surge. The Great Drake can be useful, but nothing else is really game changing for the human player from the Very Rare spells. While cool, Armageddon isn't really worth casting. On the other hand, allowing the AI to get Very Rare Chaos spells can be a disaster. Almost all of the Very Rare Chaos spells are not fun to play against and can allow a high level Chaos wizard to be quite a threat.
Life starts out very strong, but the Uncommon Life spells are lackluster, other than Prayer and Raise Dead. True Sight is one of those spells that can be critical, but is sometimes not needed.
Sorcery is like Life, in that it's Common spells are almost universally useful, but its Uncommon spells are quite lacking. However, IMO, Flight is one of the most important spells in the game given the critical effects of Flight on combat and how useful it is for increased movement. This is especially true in 1.4+, where Flying creatures won't suicide themselves, meaning that unless you can hit flyers you can't win battles, even if you have the most powerful non-flying unit imaginable vs Sprites. This, of course, is very frustrating. Phantom Beasts are obviously extremely powerful. Spell Blast is one of those spells that you may not need to use often, but there are times when its game changing. I've found that the better I get at the game, however, the less often I need to use it.
But of course Life and Sorcery come back on strong with Rare spells, both having what I would consider to be the strongest sets of Rare spells by far. Lionheart, Incarnation and Invulnerability are all insanely powerful. Any one of those spells can pretty much win you most games. Alter of Battle and Stream of Life can also be very effective, especially in setting up a new town on Adamantium or something. I really like getting Draconians on Adamantium in the mid-game with Life, because with Stream of Life and Alter of Battle pretty much the only things you need to build in the town are the base production buildings, an Alchemist Guild, and then a Stable and possibly a Shipyard to crank out Doom Drakes and Air Ships. No need to even build an Armory and no need for any religious buildings, though you may want a Shrine for Shamen.
In terms of the late game, High Prayer rules everything, and you will probably cast any of the unit buffing Global Enchantments you get, but of them all Crusade is by far the best value.
Sorcery, of course, excels in the mid-game, with a lot of powerful spells. This is when you make virtually indestructible heroes. Mind Storm and Banish are very good combat spells, although Mind Storm won't work on Undead, but BANISH WILL! This is great because its one of the very few spells in the Sorcery arsenal that works on Undead, and its quite powerful.
When it comes to the Very Rare spells, IMO, the only ones I really care about are Mass Invisibility, Sky Drake, and Suppress Magic. Yeah, Time Stop is powerful in theory, but it just not a good spell IMO. Its very costly to use, often not needed, and seems weird when you use it. I don't bother with it. Suppress Magic, however, can be great, though I do find that I don't often really need it these days as most of the AIs aren't a threat by this point. However, if you are behind in a game, this is one of those spells that can be a real game changer and turn it around for you. I'll almost always cast it when I get it, unless the game is pretty much over anyway.
As for Nature: Nature has some generally useful Common spells, but few of them are really game changers. Web is the most important of them. I use a lot of the spells when I play Nature because that's all you have to work with, but they are all somewhat middling in their effects. As for Uncommon spells, you really kind of need Basilisks to save you, and maybe you can get some utility out of Cracks Call by taking Behemoths or something, but without Basilisks at this point Nature fells like a very weak version of Life. I may have overrated Pathfinding, because often you'll have either Rangers or heroes with Pathfinding. Still, Nature's sort of ultimate combo is Pathfinding Water Walking Basilisks paired with Gorgons, until of course you can get a Great Wyrm. I feel like Nature is a school that doesn't really come into its own until the late game. The Very Rare spells of Nature are really sort of a final payoff. If you can get there, Nature has a really powerful late game. Entangle and Call Lighting is a broken combo in more ways than one. Its literally buggy in most versions of the game. In whatever version of 1.5x I'm using Entangle stops all creatures, including flyers, and it seems to stop them all entirely after the first round. Call Lightning sometimes causes the game to crash. The biggest problem with Entangle + Call Lighting, however, is that it will almost always prompt the enemy wizard to cast Disenchant Area, and unless you have Nature Mastery, they will likely get removed. But still, when in place, this is an essentially unstoppable combo that can win just about any battle, except against Magic Immunity. The Great Wyrm is of course terrifying, but the lack of ability to hit flying units is a problem. By the late game, the capitals of most enemy wizards will be filled with flying units, so this is a challenge, even if you have Web. But, with Regeneration you can now finally make use of heroes against enemy wizards, so another strategy with Nature is to build up heroes throughout the game on safe encounters, and then once you get Regeneration, put that on them and go after the wizards. I'll add that Gia's Blessing is a good spell, but for the cost I often don't need it. I'll typically have already fixed any terrain issues with Change Terrain. I do use it from time to time, though, either to speed up development of a critical town, like a new town on Adamantium, or to suppress rebels in a town with bad relations, like Klackons or Dark Elves or something.
And finally we get to Death. Death has a pretty weak opening. Most of its Common spells aren't that good. Nevertheless I do end up utilizing most of them. Skeletons and Ghouls in Darkness is the best thing to use early on. I find myself using Weakness more than Black Sleep just due to the cost, although later in the game, once you get Black Payer and more mana, Black Sleep will remain useful, while Weakness is only useful in the early game. Mana Leak can be ok, but when you are the attacker the enemy still gets 3 rounds of shots. On defense it works better, but is less often needed. Cloak of Fear is decent in the early game when going against low Resistance units, but by the mid-game its utility falls away.
Black Prayer and Shadow Demons is really when Death starts to develop. Shadow Demons are slow and clunky to use, but can be insanely powerful. I often use them in pairs, and they can take virtually any neutral town, except maybe Slinger or Doom Drake filled towns, they can win most battles against wizards on their own, and can take many lairs. If you get a stack of at least 4, then there are tons of lairs they can take when you are able to cast both Darkness and Black Prayer. Then once you get Wraiths its pretty much game over. The AI doesn't know how to really deal with Wraiths, so you can pretty much just wipe out all the enemy wizards in no time once you get them. When paired with Zombie Mastery, you basically never need to make another unit. You may need to use Wrack, especially on defense when you may not have Wraiths or Shadow Demons on hand. But for the most part, when playing Death you really only need and handful of spells. You have to utilize several Common spells to get started, but then its just a matter of using Black Prayer, Darkness, Shadow Demons, Wraiths, and maybe Death Knights if you even need them. Wrack and Death Spell to fill in gaps. If you're using heroes then Wraithform and if you both with Trolls then Black Channels, but for the most part, its all about Shadow Demons and Wraiths fighting in Darkness. In theory, Eternal Night is a good Global Enchantment, but I just rarely need it.
As a final note, here are the totals of the scores I assigned by school:
Nature: 79
Chaos: 71
Life: 83
Death: 74
Sorcery: 85
This doesn't necessarily correlate directly to the overall effectiveness of those schools of magic, just the diversity of the useful spells in those schools. Chaos and Death score lowest, but they are very powerful schools that just rely heavily on a few spells. Life and Sorcery utilize the broadest range of spells, at least in my estimation.
There are some spells, like Disjunction, that are obviously very situational, but can be critically important when needed. This doesn't do a good job of reflecting that type of value.
Clearly, Life and Sorcery have the strongest overall suite of Common spells. Almost everything you get from them is quite useful. I know a lot of people don't like Nagas, but I use them a lot and think they are worth it. Usually only 1 or 3 units a game, but they are quite potent at taking neutral towns in the early game, which is what I use them for. Chaos has the fewest useful spells, but ironically Chaos still has a very strong opening because the few good spells it has are so good that they make up for the fact that most of the other spells suck.
I'd say that Chaos in general is a sort of odd duck, in that it has a lot of spells that just aren't that good, but by the same token, it has a few standout spells that are extremely effective. It's also a bit strange because I'd say that overall Chaos has the best Conjuration game, even though most of its summons are lackluster. It really rides on Hell Hounds and Chimera, and even Chimera aren't that great. But, what makes Chaos good is the synergy of Chaos Channels, Warp Reality, and Chaos Surge. The hit and miss nature of Chaos also makes it more reliant than most on using all 10 books or at least 9 books to ensure that you get the critical spells. Honestly, masses of Hell Hounds and Chimera when combined with Warp Reality and Chaos Surge are extremely effective, especially when you throw in Chaos Channeled Paladins, Elven Lords, Golems, Barbarians or Draconians. It makes for a very interesting buildup, because the later spells actually boost the effectiveness of units you have been accumulating throughout the game and give "new life" to old units.
I know a lot of people like the many Global Enchantments of Chaos, but really all that matters IMO is Chaos Surge. The Great Drake can be useful, but nothing else is really game changing for the human player from the Very Rare spells. While cool, Armageddon isn't really worth casting. On the other hand, allowing the AI to get Very Rare Chaos spells can be a disaster. Almost all of the Very Rare Chaos spells are not fun to play against and can allow a high level Chaos wizard to be quite a threat.
Life starts out very strong, but the Uncommon Life spells are lackluster, other than Prayer and Raise Dead. True Sight is one of those spells that can be critical, but is sometimes not needed.
Sorcery is like Life, in that it's Common spells are almost universally useful, but its Uncommon spells are quite lacking. However, IMO, Flight is one of the most important spells in the game given the critical effects of Flight on combat and how useful it is for increased movement. This is especially true in 1.4+, where Flying creatures won't suicide themselves, meaning that unless you can hit flyers you can't win battles, even if you have the most powerful non-flying unit imaginable vs Sprites. This, of course, is very frustrating. Phantom Beasts are obviously extremely powerful. Spell Blast is one of those spells that you may not need to use often, but there are times when its game changing. I've found that the better I get at the game, however, the less often I need to use it.
But of course Life and Sorcery come back on strong with Rare spells, both having what I would consider to be the strongest sets of Rare spells by far. Lionheart, Incarnation and Invulnerability are all insanely powerful. Any one of those spells can pretty much win you most games. Alter of Battle and Stream of Life can also be very effective, especially in setting up a new town on Adamantium or something. I really like getting Draconians on Adamantium in the mid-game with Life, because with Stream of Life and Alter of Battle pretty much the only things you need to build in the town are the base production buildings, an Alchemist Guild, and then a Stable and possibly a Shipyard to crank out Doom Drakes and Air Ships. No need to even build an Armory and no need for any religious buildings, though you may want a Shrine for Shamen.
In terms of the late game, High Prayer rules everything, and you will probably cast any of the unit buffing Global Enchantments you get, but of them all Crusade is by far the best value.
Sorcery, of course, excels in the mid-game, with a lot of powerful spells. This is when you make virtually indestructible heroes. Mind Storm and Banish are very good combat spells, although Mind Storm won't work on Undead, but BANISH WILL! This is great because its one of the very few spells in the Sorcery arsenal that works on Undead, and its quite powerful.
When it comes to the Very Rare spells, IMO, the only ones I really care about are Mass Invisibility, Sky Drake, and Suppress Magic. Yeah, Time Stop is powerful in theory, but it just not a good spell IMO. Its very costly to use, often not needed, and seems weird when you use it. I don't bother with it. Suppress Magic, however, can be great, though I do find that I don't often really need it these days as most of the AIs aren't a threat by this point. However, if you are behind in a game, this is one of those spells that can be a real game changer and turn it around for you. I'll almost always cast it when I get it, unless the game is pretty much over anyway.
As for Nature: Nature has some generally useful Common spells, but few of them are really game changers. Web is the most important of them. I use a lot of the spells when I play Nature because that's all you have to work with, but they are all somewhat middling in their effects. As for Uncommon spells, you really kind of need Basilisks to save you, and maybe you can get some utility out of Cracks Call by taking Behemoths or something, but without Basilisks at this point Nature fells like a very weak version of Life. I may have overrated Pathfinding, because often you'll have either Rangers or heroes with Pathfinding. Still, Nature's sort of ultimate combo is Pathfinding Water Walking Basilisks paired with Gorgons, until of course you can get a Great Wyrm. I feel like Nature is a school that doesn't really come into its own until the late game. The Very Rare spells of Nature are really sort of a final payoff. If you can get there, Nature has a really powerful late game. Entangle and Call Lighting is a broken combo in more ways than one. Its literally buggy in most versions of the game. In whatever version of 1.5x I'm using Entangle stops all creatures, including flyers, and it seems to stop them all entirely after the first round. Call Lightning sometimes causes the game to crash. The biggest problem with Entangle + Call Lighting, however, is that it will almost always prompt the enemy wizard to cast Disenchant Area, and unless you have Nature Mastery, they will likely get removed. But still, when in place, this is an essentially unstoppable combo that can win just about any battle, except against Magic Immunity. The Great Wyrm is of course terrifying, but the lack of ability to hit flying units is a problem. By the late game, the capitals of most enemy wizards will be filled with flying units, so this is a challenge, even if you have Web. But, with Regeneration you can now finally make use of heroes against enemy wizards, so another strategy with Nature is to build up heroes throughout the game on safe encounters, and then once you get Regeneration, put that on them and go after the wizards. I'll add that Gia's Blessing is a good spell, but for the cost I often don't need it. I'll typically have already fixed any terrain issues with Change Terrain. I do use it from time to time, though, either to speed up development of a critical town, like a new town on Adamantium, or to suppress rebels in a town with bad relations, like Klackons or Dark Elves or something.
And finally we get to Death. Death has a pretty weak opening. Most of its Common spells aren't that good. Nevertheless I do end up utilizing most of them. Skeletons and Ghouls in Darkness is the best thing to use early on. I find myself using Weakness more than Black Sleep just due to the cost, although later in the game, once you get Black Payer and more mana, Black Sleep will remain useful, while Weakness is only useful in the early game. Mana Leak can be ok, but when you are the attacker the enemy still gets 3 rounds of shots. On defense it works better, but is less often needed. Cloak of Fear is decent in the early game when going against low Resistance units, but by the mid-game its utility falls away.
Black Prayer and Shadow Demons is really when Death starts to develop. Shadow Demons are slow and clunky to use, but can be insanely powerful. I often use them in pairs, and they can take virtually any neutral town, except maybe Slinger or Doom Drake filled towns, they can win most battles against wizards on their own, and can take many lairs. If you get a stack of at least 4, then there are tons of lairs they can take when you are able to cast both Darkness and Black Prayer. Then once you get Wraiths its pretty much game over. The AI doesn't know how to really deal with Wraiths, so you can pretty much just wipe out all the enemy wizards in no time once you get them. When paired with Zombie Mastery, you basically never need to make another unit. You may need to use Wrack, especially on defense when you may not have Wraiths or Shadow Demons on hand. But for the most part, when playing Death you really only need and handful of spells. You have to utilize several Common spells to get started, but then its just a matter of using Black Prayer, Darkness, Shadow Demons, Wraiths, and maybe Death Knights if you even need them. Wrack and Death Spell to fill in gaps. If you're using heroes then Wraithform and if you both with Trolls then Black Channels, but for the most part, its all about Shadow Demons and Wraiths fighting in Darkness. In theory, Eternal Night is a good Global Enchantment, but I just rarely need it.
As a final note, here are the totals of the scores I assigned by school:
Nature: 79
Chaos: 71
Life: 83
Death: 74
Sorcery: 85
This doesn't necessarily correlate directly to the overall effectiveness of those schools of magic, just the diversity of the useful spells in those schools. Chaos and Death score lowest, but they are very powerful schools that just rely heavily on a few spells. Life and Sorcery utilize the broadest range of spells, at least in my estimation.