Honestly this is such a zen game, I could probably kick back and play it for hours. I also can see myself coming back to it whenever I'm in a bad mood because between the colors, the song, and the cute sprites it just makes me feel really happy!
I think the only constructive advice I could have is to somehow have the play button on the title screen automatically grab focus so that I never have to move my hands from the keyboard to keep playing (gamepad controls would also be great)!