PHEW, glad I made it, it was close by the end. I had a lot of fun!
What you've done with the music syncing in this game is incredible. I'm addicted to the DING of the bell timed to the music. You've nailed the juice and satisfying feeling while playing the game.
The float movement is nice, but could use a different key to activate. It's kinda hard to position the main character where I want to on the screen without double jumping and then holding. You could making floating have a limited time/meter to make it a bit more balanced and challenging.
The enemies visual design is awesome, and arguably the main character design is the weakest, but it's not bad. I think its good the main character looks simple because it helps differentiate them from the enemies, but maybe it could be a bit more detailed and highlighted differently? I think either making the enemies more detailed or doing some kinda outlining might help differentiate enemies, projectiles,and the player from each other. Towards the end I couldn't tell the fidget spinny guys weren't projectiles, but other enemies are more detailed so it feels easier to tell.
The InBetween level upgrade screen feels like it could be more exciting. The text is clear in the weapon cards, but it could use an image of the projectile just to quickly let the player know what the upgrade is for. Since there's space under, you could make the cards bigger and space them out more to make the page more visually appealing.
Maybe to balance better, the weapons should cost hearts, and you can still replenish hearts with the time? It did feel like it was easy to be OP very quickly, this could help curb that.