A very challenging game! The visuals are very smooth and clear, though it might help if the player had a color to make it more distinctive from the roads. The music and sound effects are very good, too.
Criticisms/Suggestions:
I had a hard time getting used to the controls - the slow acceleration/deceleration and the turning. There could be some easy tutorial levels where you get used to controls and other mechanics (doors). Just getting through that first U-turn in the beginning of the level took a dozen tries.
Clarification with some mechanics would help, too. In the second level the last door was closed and I have no idea why. Didn't see any buttons down there either. So I couldn't beat that one.
I haven't played Super Monkey Ball, so maybe I'm just be lacking knowledge and experience of the genre.
It is a well-made game though, and feels very polished!