I think the art in this was just fine! The music was a short loop, but it also worked well since this is a pretty short game.
The player can only attack monsters when moving to the right. This is a weird mechanic for a game to have, and there's no reason to expect it, so it's hard to tell whether you did it on purpose or not. The space bar makes the character tilt, but I don't notice any effect. Maybe it has to do with the flying enemies? I can't tell. It's possible that you could solve both those issues with some instructions about the controls.