Hiya! First off, wanna say that I've really been enjoying this game when I'm bored and want something mindless to play. I've finished numerous songs with full combos and have found it incredibly fun to come back to :D
I come with a suggestion, and that's to add a "random track" button somewhere on the song picker. Sometimes I really don't know which song to play, and I think it'd be nifty to have the game pick one for me. This would be up to you, of course, but maybe we could set it to pick from a specific chapter(s) or the entire track list. Just a thought.