So far I can recommend Sonic Before the Sequel 2012 and The Emeralds Awakening, and GHZ 2.5D as a proof-of-concept. Most of the games are naff, but you can get your classic Sonic fix all the same.
That sonic 2.5D was wonderful, i would love to see it in it's entirety. even though it's just a small difference from the original game, i could see it being something any fan of sonic could really enjoy. i also played AXSX which is a re-imagining of sorts of Sonic X-tream. it's trippy and fun to run around in, but nothing more. makes me want to play nights though.