Starting to get into the swing of things with creature gen, finally, and the approach I'll have to take on this is starting to make sense. Of course, it's also becoming clear that this is going to get REALLY complicated, but... what the heck, that'll make it more fun.
Things I'm currently thinking about, both short- and long-term, and attempting to implement:
* Creatures should fall most prevalently into Earth-similar norms (i.e. no multiple heads, fairly sensible body arrangements, and so on). The reaction upon seeing new creatures should generally be 'woah, neat, what's that?'. A rarer amount of creatures should fall mostly or completely outside of earth norms (multiple heads, many-legged/armed vertebrate, pincers on a mammalian-ish creature, subterranean creatures with beaks, tentacles, and fur, yadda yadda) and should induce at 'WTF!?' reaction. Of course, creatures should also possess some rare traits that are more magical than morphological.
* Creatures need not be particularly interesting to be useful. Something like a sponge, which is seemingly useless and defenseless, might possess morphological traits which make it drop a useful item upon death (dye, processable skin or organs, medicinal substances). Similarly, larger creatures should drop appropriately relevant items depending on their traits. These sorts of items should eventually make it into cultural references and item creation/economies.
* I should probably also think about unique plant/tree generation, though this will be a headache because it will require the recoding of certain parts of world gen.
I will probably release a new tech demo soon just so people can play around with the up-to-date worldgen as it stands. Even though it's rather useless at present, the maps do make rather nice desktop backgrounds.