This was a lot of fun! There's no shortage of Zombies in video games, but you've found a really fresh take on them. The loop is simple and easy to learn, but still stays enjoyable to play over and over. You've built a really solid foundation that I think you could use to flesh out this concept even further. I can imagine this game having more levels, co-op and competitive modes, powerups, different zombie abilities, more threatening humans, and more. Even if you never worked on this again though it's wonderful as is. Great work!