Great game! I liked how the zombies were all over the place forcing you to try to figure out which of the zombies were the real threat. The art looked great too! A couple easy ways to refine it would be to change the height of some of the zombies, add some zombie noises and/or add a hit graphic/particle effect when you shoot a zombie. It worked great as a fun mini game that didn't need a bunch of instructions, well done!