Spin to wind is fun. Good enough for me to play every level. Perhaps level 15 should be the last one? It seems to be the hardest.
I think you've got it down already. The game is good. One of the few things I can imagine to step it up a notch would be to add some dynamic elements. Something that moves across the course to dodge? A lane of cars you have to slip between? Something bouncing around that can knock you out? A spinning something to knock you off course? As is though I think your game already does the whole "entertain for 5-10 minutes bit" though. Very well done. I had a good time with it.