Nice entry! I like the pixel art and the music. I caught one bug --- if the time between waves runs out while you're interacting with the shop, you sometimes lose the ability to shoot.

Doesn't seem that you can aim down or up meaning you will only be able to hit the zombies from either the left or right

The some of the upgraded weapons don't seem to be anymore powerful (Shotgun), fires slower, and takes longer between shots

There were times when the controls cut out not sure what the reason was. WASD stopped working (though the arrow keys did work) and I was unable to fire or reload any of the guns.  This happened for 30 seconds or so and then the controls started working again.

Music, art, and idea were all pretty solid otherwise.

Undoubtedly the game that I had the most fun.

Thanks for this game, I appreciated. I love kill some zombies

this is game amazing...