Good idea, but the execution could use some work.
Your player is too slow, there aren't enough zombies to make you feel like you're ever getting overwhelmed, you still kill zombies, just with bombs instead of guns to name a few.
The idea of blocking the zombies instead of shooting them is great. The game could be expanded with things like boards to climb walls, and grenades which cure the zombies instead of killing them so you have an objective and more distractions for the zombies.
The concept has potential, but still has a ways to go to live up to its potential (fair enough since you only had 48 hours).