Alright....
It's good, but gets pretty monotonous fast. It might be better if there were a larger play area, and perhaps some environmental objects to use against the zombies (exploding barrels, or something like that).
Also, shooting the zombies wasn't terribly satisfying since there was no change in their momentum when you shot them-- if I shoot a zombie with a shotgun, I'd like to see it fall backwards a bit. This would add to the realism of the physics, and would also provide a little reward for a direct hit (the reward being a few extra moments before the zombie is on top of you).
But nice look, and fun enouhg.