Its pretty good, but there are some minor problems:
1. run(on flat ground) and jump towards a slope, and sonic will start to go through it, but not all the way.
2. Accel and decel on slope.
3. there NEEDS to be diagonal movement.
4. (in special stage) jump on the flat part and move towards the slope, sonic will start rising more than the jump would normally make him.
But, those aside, its awesome!
keep up the great work.