Cool idea! Brings a lot of the nostalgia from the era and things like Guitar Hero on early mobile phones. I also really enjoy the low-fi vibe of it. The small emoji dancing made my day for sure and it's fantastic that you can already track the score and combos :)
I do think a lot could be expanded, my only "issue" was the UI was a bit awkward for today's resolutions (too tall), but I'd love if you could add keyboard support, feels like it would play fantastically on numpad!
Also very thankful for your insight on the rhythm chart, learned a lot today.