I like a game that has simple controls and offers up a cool way to implement them. The beauty, as they say, is in its simplicity. I also like the look of it, like something that was drawn during school, maybe started as a school project and become this long doodle.
The music speeding up and slowing down is a natural extension of the game, but I'm not sure how I feel about it as a soundtrack, and it can be distracting at times.
Original take on the control of speed-in this one, you're controlling time.