I think there's a lot here that's great. But once you knew how to jump farther, stopping to play the song every jump became a frustration, slowing the game down. Also, I got completely stuck and had no way of restarting the game when I got to a wall on the top.
I really liked that you have access to all of the songs from the beginning, though only after you got the harp and that by replaying you could get access to areas you didn't know you could get to before. Reminds me of Toki Tori.
Z to jump is strange. I understand that on other keyboards, such as German, it is above the S, but I didn't realize that you could change it for a while. I do like that you put that option in there. That was a nice touch.
Good job all around, though!