I am really impressed by what you created here. The artstyle, the music, song mapping, the feedback, vfx, everything works together perfectly and is yet so simple! Brilliant. It creates a really satisfying experience. Most significantly the well-placed sounds of the song that serve as additional hit feedback.
I also like how you start simple and then, much later, introduce the twist in the mechanic with the triangles where you have to actually press the opposite direction of the incoming note. Great pacing.