I liked this, seen a few games similiar to it but at the end of my playthrough a bunch (like 10) zombies spawned exactly where I was and I stood no chance at all.
Any chance you could alter the spawn and make them further away, could also add some powerups and such to vary up the gameplay.
I only suggest these things because you said you wanted to upload a fix for your bug after the jam, figured you might want to continue working on this project.
It has some solid artwork i'll give you that but since we were told to judge on design i'm focusing on that for this jam :P
Regardless nice product you have here could be a nice browser game if you finish it up a bit.