This game is really cool. I feel like i'm playing as the ball in a pinball game, it's really fun, and the graphics and the sound only had to that.
If you wanted , you could really expand on this theme and make the setting an actual pinball machine.
I don't know if you had already considered the idea, but i think the ability to do a little jump with the ball could be fun too.
The only I'd check is the rewind, sometimes it acts a little oddly