I like the art style, it is pretty clean and the animations are good. I especially liked the particle effects.
The sounds were good as well. And I don't know if you guys made the music or not, but it's amazing and got stuck in my head xD
While the gameplay is fun, but maybe could be a bit more fun if it was more challenging, the zombies were faster and the player was a bit slower. Also, you should maybe destroy the shots when they are off the screen to stop the player from being able to kill enemies off the screen.
All in all, a really good game for the small time limit we had, congratulations and good luck in the game jam :D