I find Troll shamans a strong strategy on higher difficulties. Thanks to GermanJoey, I have become aware of the Troll Magicians Focus Magic strategy which is (if you get that far) hard to stop. However, it takes you rather long to get there.
But in the meantime, shamans do really well. They have the same structural benefits as Troll magicians (high defense, hit points, regeneration). Best of all, they get really strong really easily (Orihalcon; Adamantium) and are comparatively cheap, especially with Coal. If you have all these three combined in one city (granted, it is rather rare), you get cheap, strong and versatile units. On top of regeneration they mutually heal each other. Out of ammo? Come get some melee! They can still be improved with easy spells (Focus Magic works well on them, although obviously not quite as well as on Magicians), but even all the other improvements (Holy Weapon, Eldritch Weapon, Heroism, Wraith Form, Eldritch Weapon) are useful even though they only work on the Melee part - because you are not afraid of using them in Mele if properly buffed. The death strategy makes this even cheaper, but it could also work with the sorcery strategy (build shaman stacks to strengthen your empire and lay the foundations for a magician focus magic assault). Corruption as a countermeasure is less effective due to the inherent ability of Shamans.
Of course, the same arguments go for everybody else's shamans - but there you have the fragility issue.
But in the meantime, shamans do really well. They have the same structural benefits as Troll magicians (high defense, hit points, regeneration). Best of all, they get really strong really easily (Orihalcon; Adamantium) and are comparatively cheap, especially with Coal. If you have all these three combined in one city (granted, it is rather rare), you get cheap, strong and versatile units. On top of regeneration they mutually heal each other. Out of ammo? Come get some melee! They can still be improved with easy spells (Focus Magic works well on them, although obviously not quite as well as on Magicians), but even all the other improvements (Holy Weapon, Eldritch Weapon, Heroism, Wraith Form, Eldritch Weapon) are useful even though they only work on the Melee part - because you are not afraid of using them in Mele if properly buffed. The death strategy makes this even cheaper, but it could also work with the sorcery strategy (build shaman stacks to strengthen your empire and lay the foundations for a magician focus magic assault). Corruption as a countermeasure is less effective due to the inherent ability of Shamans.
Of course, the same arguments go for everybody else's shamans - but there you have the fragility issue.