Small complaint: the only time you can see the attributes of the special humans (when you unlock the first red upgrade), they cycle through so quickly you can't really read them. It would be nice if there were an encyclopedia or something where you could read their abilities.
It would be nice if you ramped up the difficulty a bit. I got as far as level five and was just bored of it. The first several levels just felt like filler. I have no idea if it gets more interesting after that, since I didn't want to devote another 20 minutes of my time to such a laborious game.