Really fun game! Loving the artstyle! Good music, cool gameplay. I found a glitch though. When a zombie hit me multiple times, once, I stayed in an infinite knockback state and stuck in the wall.
The score board after stages are really well done. Having bonus stage is a good thing to add more variety. Collision handling needs some work, also sometimes I shot their head when I was hitting their legs (if we look at it from a 2D perspective).