I feel that they are a bit redundant now that we have werecreatures. Do we really need two different kinds of human-animal hybrids? Add to this the fact that they don't bring much to the game, just more creatures to kill/be kileld by dwarves. Personally I am OK with possibly a few generics like 'birdman' or 'rodent man' because such things are rather generic. A rodent is a pretty broad term, and encompasses the idea of a humanoid rodent rather well. A 'mooseman' on the other hand, is a very sepcific animal. I think that after a while, there comes a point where it becomes a bit strange. Do we really need animalmen versions of every specific species of animal? Before you know it, we will be having subspecies animalmen. I'd personally rather not run into the likes of poodlemen or the like.
I feel a bit similarly about many of the giant animals. Giant spiders and Giant scorpians are pretty fitting, I think, because they are generic animals, but a lot of the giant animals are specifically giant species of existing animals, which is somewhat annoying. Personally, when I mod, I try to remove a bit of this sort of thing. There are plenty of animals, real and mythological, that are unimplemented which would go well into [SAVAGE] biomes. For instance, I modded in Aurochs and Tarpan (wild oxen and horses of the type often depicted in cave art) for savage biomes, and wargs as an [EVIL] counterpart for wolves. Considering many of the outlandish creatures Toady implemented for the underground, I'd say that this is definately not due to a lack of imagination, but I do think that the animal/giant animal/animalmen system is a bit bland way of handling things compared to the imaginative ways Toady has handled other parts of DF.