I think everything in this game ranges from fine to pretty good. What I would work on is making the jumps slightly less floaty, maybe implement a double jump to jump over boss attacks rather than a single jump that goes that high up. I also think the second boss is underwhelming. I quite like how the game looks, and I quite like how it sounds.
The game does not incorporate the jam's theme at all, which isn't a deal breaker, but it does negatively affect the games score.