Standard Physics Shooting Game - But too easy
Overall: Much like many others out there.
I would have rated a bit higher except there is a significant flaw in the game. If you run out of missiles the level is viewed as failed - although there might be the possibility of the zombies still being killed by a rolling boulder or such - this happened to me on two levels. There needs to be a timer to wait a few seconds to allow all actions to complete before failing a level.