Nice work! Not only was there a game with a challenge and a final boss, but you also have key-rebinding, different game modes, and instructions in-game. There's actual polish here, which I'd take as an indicator of good scoping and time management for a jam.
I'd echo the feedback that the game lacks visual clarity. I'd also like to see the theme play a bigger role in the game mechanics. As it was, I didn't see a point in trying to engage any enemies, so I just stayed at the top of the screen until I got to the boss.
Congrats on your first submission. I look forward to seeing what you make next time!