Not a bad game. Simple but fun. The problem I had with the game is the size of the play area. The zombies move incredibly fast , and because the area is so small and the zombies come from every direction, it's practically impossible to avoid taking damage. When you get to a certain point, the waves of zombies last even longer making it difficult to survive. I understand it shouldn't be too easy, but even with all the upgrades from leveling up your character, and weapons, it gets ridiculously hard. I found myself only upgrading my health, and damage with the exp points from leveling up.
Aside from my complaints, I think the game is rather nice. Keep up the good work.