This was more fun then I expected! There are a couple of things that make things tense for the player (and that's a good thing in this case!)The rate of zombie spawning combined with the rate of fire and taking care of patient X, keeps you on your toes. It's very easy for the zombies to form a horde and that's when you need to duck and weave like crazy. Plus the zombies arms coming out of your peripheral vision is a nice touch. The building blocks are here and I think with some more time and polish this could be really cool! Some more building and obstacles, maybe add the ability to board up areas and make it a bit easier to get Patient X what he needs, I think you have a good thing here. Nice job!