Honestly, it felt really good at max difficulty, challenging but still fair. I think it's perfect for a jam.
But since I do see you're building a wish list for a steam release, if I had to suggest anything, maybe justa bit stronger feedback on timing? Like clearer "perfect / early / late" distinction or slightly more punch when you nail something dead-on. A few moments also just slightly felt visually off when multiple notes hit together, but nothing that stopped it from being fun.
Overall, though, it's in a really good spot. You've got a great base here.