Overall the concept was interesting. I made it to the second level? (the music changing level) Also I rather enjoyed that you could change the octave of the music even if it was more of a cool mechanic and not related to the game. If you implemented such a mechanic, I would suggest making that integrated with your game somehow.
The only thing I suggest in the short term is change your collision area. Either a) make paths a bit wider, b) make the characters smaller or c)change the size of the hitbox to the path. When I got to the music change level I tried to get past the slippery sand and they collided with the wall and were unable to move anymore. I saw you can press R to restart the level but it failed on multiple occasions.
Also, your in game instructions don't say to use spacebar to interact so I didn't understand until I went back to read the page.
Keep up the good work!