Good start
I'm impressed with what you have here, but it's not really that enjoyable to play, due to a few flaws.
- tbe jumping is a bit messed up when Sonic's on a side or on the top, as are the 'physics' in general. He shouldn't be able to jump off the top and return to the top - it should make him fall to the bottom. Also, he should fall off the wall or sides if he slows down for too long.
- The game doesn't seem to get harder. You should have more obstacles appear as you get more coins. This is the biggest problem imo.
- As the reviewer below said, an animation for when you lose would be good.
Still, as I said to begin with, it's still an impressive wee thing, so well done.
Stay funky,
Bez