Props to you for developing in pico8!
I think the biggest thing this game needs (besides music) is some visual feedback. I can't really tell whether I'm hitting the notes or not, with my only success indicator being how many stars I get at the end. Indicators like a big colorful splash effect or a "Good!" pop up or a nice satisfying sound when I successfully hit a note is the lifeblood of these types of games.
There are some other weird choices that I think are really fighting with some genre staples. Like having the arrows ordered as [^v<>] instead of [<v^>] fights my natural intuition. And the core mechanic of having to wait for a random roll in order to hit a note correctly really detracts from the rhythm aspect.
That all said, I real appreciate you for putting something unique and experimental out there. I know making anything at all happen in pico8 is challenging, so submitting a finished product at all is impressive. Keep at it!