I'm impressed.
Damn fine game. Anything of the zombie persuasion gets the benefit of the doubt, but this game would have been a good one even if it wasn't zombie-themed. My advice to make it better? Make it longer. It's already exceptional, but if you make an extended version - say, 50 days - and maybe throw in a new weapon or two (I vote minigun as the last weapon, or maybe make it a hidden one), that would be great. In my mind, that's the only modification this needs. Keep up teh good work!