For your first jam its quite an achievment, well done!! I like the visuals and I think you need to explain fuirther how to play right, I rate graphics on top of everything, but all is fine, also if you have time please check my game, thanks!!

This looks like a good start to a cool idea. I couldn't figure out how to defeat the boss so I just kept jumping around hahaha.
I would include some notes on how to play or next time provide a small tutorial for the player. I see that this is your first jam contribution so congrats! I would keep this game around to look back and see all of the progress you've made in the future. Keep it up :)