Freedom Planet
This fan made is awesome! It had a interesting set up and follows the great classic-Sonic formula of gameplay. Of course it's only on PC/MAC but I'm sure they plan on going to consoles.
Of course I fear that this will be an excuse for gaming purists to bitch more about "How Sonic should of stayed 2D" when he could finally get his new 3D stuff right.
That being said you should try it cause there is a playable demo.
Update: Just beat the game and I must warn you it is HARD. Best to start on easy and not normal the first play though.