Very cool artstyle! I can't stress this enough. If you made these graphics yourself, congrats: They look awsome!
The game itself feels very solid and polished.
My only piece of constructive feedback is that the pacing is too slow. I wish I could speed up the time sometimes like in Bloons TD. Also, the enemies were weak enough to be defeated by my mouse, even when I was several levels deep already. There's not enough ramp up.
But don't let that discourage you. I think you did a great job and this is wonderfully well presented game