I liked this game. It was fun. It seems like it was a good little thing (which most flash things are anyways). If you want to improve it, you could add shops, ramp up the difficulty, add in more zombies, possibly even add the goal of creating a base from the zombies, or, if not, make it possible for the player to explore new areas, which they could be forced to do so by making new areas the only places for reloads. Also doesn't seem to have any bugs, so good job on that.
Seems buggy (too many to list) and needs revision. Would be nice to have a flash version of Clash of Clans where you can upgrade things quickly, so it's a creative idea.