If this Sonic doesn't work out... I suggest a radical redesign:
First Person Sonic.
Now, before anyone goes off, let me explain. See, I was watching videos of someone's coasters they created in Rollercoaster Tycoon, and I thought... THIS is what 3D Sonic should be like. I mean, Sonic's old games were basically like coaster rides – high-speed, loops, hills, corkscrews, etc. Imagine running into a spring platform at the bottom of a hill, and it rockets you to the top of the hill, where you teeter for a moment, and then plunge headlong down the hill at breakneck speeds, a chain of rings giving you a path to follow, then flying off a ramp at the bottom of the hill over a ravine, adjusting your trajectory a bit to collect rings in the air. You land on the other side, and are going full blast and tear into a tube. You're going so fast that you can run on the walls and even the ceiling, and you HAVE to do this to avoid spikes on the ground.
Since all of this is in first person, it'd give you the feel of a roller coaster. Just thinking about a Sonic game like this gives me chills...