I like it!
Well, I think, you've made a good game.
I liked that I could myself beat those little bastards, and also the style was good.
But, there are too few kinds of towers-only 4, and in the beginning, the game is too easy, in the end-too hard, it makes the gameplay boring.
Also, the game has a strange upgrade system-instead of upgrading the tower to the second level, you can spend this sum of money on 2-3 new towers.
Howerver, I find this game great.