Very nice!
My only recommendations are to get a nicer font and some 'full-' keyboard controls:
- E.g. WASD and have full-keyboard menu controls (so you don't have to use a mouse). Things like a menu cursor for arrow/WASD key movements and using enter to go next or accept would make it 5-fold nicer and more polished.
Gameplay, however, IS GREAT; the shift 'mode' was not the most intuitive if you don't read the itch.io controls part (but just writing "Hear Track Preview" will clear the mud).
Love to see an open-source project too!