This is one of the few games that I want to keep playing after the game jam is over. It's just that fun!
If you continue on this game (and I hope you do), I would like to see a better beat system. I like that you can go at your own pace, it allows you to plan ahead. But there's also no reason to go fast per se, since the only thing that decides your buildup rate is how fast you press space after the final note. Try making the first two notes set the BPM, and base the buildup on how on-beat the following notes are? It's just a thought, and doesn't detract from the fun I had in the game.