Not too bad.. Plenty of scope for improvement.. different types of bullets bouncing, non bouncing, ones that go through more than one zombie. Possibly grenades or different types of guns?
Like the exploding terrorist zombies could do others that can only be done with certain bullets or maybe some non-zombies that you have to keep alive or stop them from being eaten by moving targets, which would introduce a time scale to your actions and thoughts.
Massive scope for the game hence 3 stars now, so there is room for improvement.
Good game though keep up the good work!