I have no idea why no one has commented on your game, but I think it's a really good game! There are issues with the difficulty, and I think way too many zombies spawn for how little ammo you get and how many bullets it takes to just kill one human-zombie (didn't even kill one of the green dudes). But the graphics are good, the story is good, and I think it fits the theme, it could definitely use some audio, or at the very least some music, but overall to build this alone is really cool and you should be proud of yourself!