A few comments:
- The cheat sheet looks pretty blurry and hard to read
- It might be better for the game to pause while referring to the cheat sheet, and that you only have to press H to toggle it rather than hold the key down
- Tutorial says "use W and D for single player movement" when it should be A and D
- Tutorial could move at a faster pace, or perhaps have Next/Previous buttons to navigate at own pace
- Tutorial just gets stuck at "Good Luck!"
It might be better to add a key short cut for switching, like pressing s. Seems weird to suddenly have to click a button for that stuff.
Also it's not super obvious that the wooden blocks can be moved by the clicking either. And that you can click + drag around to view the level. A brief mention of that in-game might help!
Have you found any music for your game yet, by the way?
However I could suggest using another instrument besides the piano, because when there are multiple notes at the same time, especially for solid lines, it sounds really jarring due to the dissonance. Maybe something lighter like pizzicato strings? :P
Reminds me of Z-Rox (http://www.kongregate.com/games/EvilDog/z-rox), except instead of seeing patterns you're hearing them. Still, it's a pretty interesting concept that hasn't been done before! And at least we get to see the complete shape once it's been solved :)
Easter egg at title screen: all the boxes in the above screen are movable and the arrows can be moved. Furthermore, changing the direction of the green arrow on the box in the title itself causes all the other green arrows above to follow that direction! Nice hidden feature :P