Controlling two first person characters in tower defense is an idea I haven't seen and it was immediately intuitive. I had some trouble coming up with a way to use that in my favor though - since I was always just targeting whatever slime was closest to me, I didn't get much of a chance to use both characters at once in any useful way. It could be cool if you added a way to freeze one of them in place so they can keep shooting at one horde while I control the other one to take care of another.
Super unique concept though!