I love the graphics of this game so much. I really like the background. The music is also really nice.
Your theme interpretation. Musical scales! I didn't even consider this and I am a musician. Great work. It was a nice surprise finding the clefs as well as notes.
I would love to see this developed with a narrative of some sort. I do think the walking could benefit from a run as well. It may also be a good idea to have a more explicit indication that the clef is the problem in certain melodies.
Great work.