Good job getting the game out! The sound effect for shooting is good and I like how silly the art style is. I also like that you can loop from the top to the bottom and from side to side by going on the edges classic mario style.
I wish there was some way to see how long before I can shoot again. The slugs staying alive when they hit you is brutal since one gets on you and you just die. A score would be a welcome addition as would a variety of enemies. You'll see a lot of success if you made a web build for your next jam.
Good job!