Great idea!
I first need to realize that "holding left" meant actually pressing A or Left Arrow...not Mouse. I thought the game was broken at first :D
The shooting works, but the initial spawn time of the zombies is a bit too long I guess. The art style feels like being a prototype. The worlds look kinda empty, but the characters look really great! Especially the title and defeated scene look very nice. Would be good if there was some more consistency in the art style used and I recommend using a certain color palette for things, as well as using certain sizes for text in the UI. The music is fine, just like SFX, but I guess they do not fit together that well.
Still overall a good entry to the jam!