Played your game, and it was really nice! That said:

• I think the song selection could also use a difficulty rating, so that players can work their way up, rather than immediately being crushed by the harder songs (like me xD)

• The way the game fits the theme, it would be nice to have a visual or audio feedback after hitting the notes perfectly, or if they’re hit with delays (pun intended)

• Lastly, I had difficulties in using the song editor to play some custom music and feel that

    1. Calculating the BPM of a song manually can be a hassle sometimes, so a way to calculate BPM automatically when you select your song would make things easier for the user.
  
    2. I had no idea what the beat offset field did (and found out what it did sometime later xD), so documentation on what that does in the song editor would be better for players wanting to play custom songs in your game.
  

Those are my 2 cents. Other than that, amazing music, great gameplay, awesome game.