Good game, a few issues though:
1) Flying zombies are invincible during flight and block all shots fired at them, only one of these needs to be fixed
2) When you can get through the entire game with only the pistol it's too easy.
3) A description of the weapons would be nice, and maybe stats as well.
other than that it was a fun, albiet short, game. 4/5
Biggest issue I find is that the HP of the enemies rises faster than the damage of the towers. Another issue is that the reward for killing enemies is fairly low, meaning that I need to save up for multiple waves to buy a single tower.