Wow, that was cool, and hard lol I failed at first. When the first game started, I missed a bunch of notes because i simple didn't noticed that the game was already on (I know, silly me). So maybe a call to action there at the start would be good.
The boss battle got me unprepared with all the notes and super speed lol (I kinda cheated though, spamming keys as there was no punishment for wrong notes)
Maybe add a small punishment for wrong notes would be cool too.
Oh, and the music was super loud, but you had volume controls! I think it is the only game in the jam with volume options, it is really useful.