Here's my idea:
Mark of the Wild TD
Either you have i dialog where you choose race or you do something else...
Well the races are.
Bears
Boars
Dogs/Wolfs
Cat Animals (for example, lions, cats, cheetas...)
Bugs
etc, etc...
And stuff like that.
The diferent sorts of animals should only be built at their natural enviorments (look picture).
The enemies you are defending against are humans that hates animals/bugs.
There are four types of humans coming, one from the top, they are weak against ice/snow animals, the ones from the left are weak aganist grass/forest animals, the ones from the right are weak against desert animals, and the ones from the bottom is weak against savana animals (look picture).
All towers has the ability to become a free animal that walks around and kills humans, but that costs 1 food and you only have 5 food, this amount can be incread to 10 but thats expensive.
Modes:
-AP = The usual all pick =D
-AR = The usual all random =D
-LM = Leader Mode, The host chooses races then all will be able to pick them.
Add on Modes:
-FG = Fast game, only half levels
-EM = Easy mode, humans have half hp
-HM = Hard mode, humans have double hp