Great little game that gave me a few minutes of joy while playing.
The only issue I had was that the game would crash whenever I killed a lucky zombie. This may be because an unhandle exception. In the unity editor this won't instantly kill your game but in the built version it does. It happens to the best of us (and me too, but I am not even good).
I just took it as a feature. The green zombies are fourth wall zombies that when killed take revenge on your game. Just avoid shooting them (: