Boy, this demo is rough. The opening levels have some promise, and I actually enjoyed learning to S-Rank Area 99, but things immediately nose-dive with Wild Ridge and never really improve after that. Wild Ridge fails because of awkward plane controls and overly-punishing obstacles, and White Jungle is a round hole that the developer is trying to shove the square peg that is the Infinity Engine into. The levels after that moreso suffer from poor conveyance of direction and pacing. Exploring can get me lost, and trying to go fast can get me killed.

The game is still in development though, so could it improve? I don't know. It looks like they're only making the later levels now, and seeing their ideas for how to make Sonic levels more difficult doesn't fill me with hope.

Edit: The final game is out. It did not improve.