Great game, a whole lot of fun. Just one suggestion, though: Though the early game is pretty tough (especially because getting multiple shots on those damn rabbits is hard), by the time you reach the maximum level, the game becomes pretty much unloseable for even an OK player. By the time you get the minigun, you're just waiting to repair the car and get right out of dodge; there's no way to lose because you can buy a medkit for basically nothing by that point, meaning you have nearly infinite real health. If you make a sequel, perhaps you can integrate a system that makes medkits and mines progressively more expensive in the endgame to make up for all the money the player will be making.
Again, though, this game is a lot of fun to play. Looking forward to a sequel.