The biggest disappointment is that it ended. Put together a tutorial and a few dozen levels and it would easily be worth $5-$10 on steam. When I beat the first level and saw 1/4 notes filled in, I thought it was a ranking system so I was trying to get a better score by using fewer notes or holding keys down for the least time possible. Only to realize it meant it was level 1 of 4 completed. Might be harder but a ranking system based on the total amount of time notes were held or total number of notes placed would be great for replay value.