What a fun mod!
I guess I can chime in with the "animal balance" concerns crowd. They're a little out of control, much more frightening than anything the barbarians (whether orc or demon) can come up with in the earliest stages of the game. Limited exception might be lair bosses could compete with nasty griffins or other high STR and/or moverate critters.
Tangential to that, I think mostly about "beasts", is one thing I'm a little confused about: the "Slumbering" promotion. Kill something and fall asleep for some random number of turns? It didn't make a great deal of sense to me. The main way I encountered it though was by building Pact of the Nilhorn and being disappointed that the Stooges would smack something, then fall asleep and need guarding for some unknown number of turns. Maybe this Slumbering business is meant to give humans and AI a fighting chance against certain critters, possibly including the Stooges, but it didn't make a lot of sense to have formerly useful units come down with narcolepsy. Anyhow like I said, I'm not sure all of what's behind this negative promotion, maybe it's dispellable in some sense that I haven't gotten around to yet, but it was an odd thing to have to contend with. I haven't yet captured any Beasts, so am not sure if it could affect more player units than just the Stooges, but I'll keep playing and see what happens.