Pretty fun concept, but rather buggy and unpolished. As far as bugs go, I've found three major ones immediately:
1. When two zombies walk into the same tile, one zombie disappears (game seems to treat it as one zombie then)
2. If you hit the wall, you die
3. If zombies hit the wall, you see them on the wall tile, then flash back to the previous one

If the bugs are worked out and the game gets polished up, it'll be pretty good!

A challenging game. Simple. Fun but frustrating. Not the best graphics but they work for this game. Needs something to make it more "wow". Overall, not the worst, not the best, and it could be a bit better.