The upgrades system is such a brilliant addition to a rhythm game! I love how depending on your skill level, you can either make it easier for yourself or add challenges to reward skilled play.
Also, as a musician, I have to say the way those upgrades/additions affect the music is awesome. I absolutely love adaptive music - it’s a musical style only video games can do - and this is a great way to do it, affecting both the gameplay and the audio together. The song builds throughout the game too, culminating in that killer key solo at the end!
Speaking of that solo, though… I think the difficulty curve could be smoothed out. Most of the game is relatively simple - not in a bad way - but as soon as I added the solo, the game introduced two more lanes and drastically upped the complexity of the map. As a relative amateur at rhythm games, it was a little dispiriting to go from something I could reasonably sight-read to something I could barely parse. (Although I did get over 80% somehow?) I don’t mind the hard difficulty at all, but it might be nice to sprinkle it in earlier rather than backloading it. Doing that might also increase the feeling of a roguelike, because I didn’t actually find myself dying and having to go again, try different upgrades, etc. (Shame, because I didn’t get to add all the musical layers in in my run… I wanted to hear the guitar part!)
Great work overall! The music is an absolute bop :)