I liked the concept! Some thoughts from me:
1. The game was fairly fetch quest-y but I think even the fetch quest format could be interesting with more storytelling around the instruments/people involved.
2. The rhythm game part was fine and straightforward but would get repetitive fast. I have like a million hours on Crypt of the Necrodancer though, which has lots of novelty in it.
3. It could also be interesting to do something like Terry Rileys's "In C" (or perhaps more interactively "In Bb" https://www.inbflat.net/ ), have you considered it? Though I did like hearing some of the parts line up together too.
Thanks for your comment!
Yes this whole thing is tricky because I kind of do want to make the unapologetically difficult version but then I am worried it will be too hard for most people to play, but then the people who do stick with it and make it through might find it even more satisfying. So it's a tricky one!
I hadn't heard of Terry Riley until just then but yes, that is very much in line with what I was going for! There's something just fascinating in itself about hearing individual lines of music come together, it's a reward in itself, and it does feel like someone should be able to make a game around it.