The bonuses it provides are absolutely obscene, though it does limit you to some of the worst food items in the game. The inability to kill animals isn't a problem in my experience, because you can make animal friends, who will kill the passive non-retaliatory animals for you, netting you experience. Though I honestly feel that if you take it, it should be maxed out IMMEDIATELY, to reap the full benefits of the skill tree, since you face the full penalties right away as well. Certainly the first skill you should take is animal friend, because otherwise navigating the dungeon becomes nigh impossible. What do the more experienced players think about the skill? Does it doom whoever picks it to failure later on, or are the penalties rendered meaningless by some endgame strategy, making you invincible? Or is it actually well-balanced?
Vegan + Vampirism (since you're limited to the worst food options anyways, this is a natural fit) + Blood magic + promethean + <insert spell category here> + burglary + archaeology / Observation This sounds like a fairly valid route, really. The only things you'd have to watch for is the AE damage causing mass stacking of negative vegan buffs, but in theory the top level skill allows you to clear that I think.
If you kill an animal with a spell, just give them the old "I was nowhere near him. Someone else must've roasted/acidificated/decrepificationed/transmuted-into-gold that poor critter.". In other words, vegan for survivability pairs well with spellcasting.
I generally use it in my non-magic builds, because I'm hoping that the ludicrous stat bonuses it provides will make a warrior build viable. Sadly I've been unable to test it much, because I use a mac, and the current bug prevents me from continuing past floor 1.
