love the concept but, the art needs a rework and the audio is a bit lacking, the zombies are a bit too fast and they are spawning too fast so it's not really fun, a bit of polishing is in order like a score system or the zombies like rather than going straight for the players it should go in one straight line in one direction and do a 180 turn, might also want to add small touches like camera shake or blood splatter.
good job :D