This might be a bit old now, but it is still alive.

In October 2016, a fan made the first and only 3D Sonic game which actually plays like Sonic. It is only a demo of one level, but it is a big level and really beautiful marvel

See here: http://www.pcgamer.com/sonic-utopia-is-a-fan-made-open-world-sonic-the-hedgehog-demo/

This looks NEAT! And like copyright infringement! But if Sega knows what's good for them, they'll boost his drive to create a worthwhile game that includes Sonic The Hedgehog.

Okay, Sonic Generations wasn't too shabby, but there hasn't been a decent Sonic game since the Sonic Adventure series imo. They should have stuck with 2D platforming.

Gameplay - https://www.youtube.com/watch?v=BsGiXBxDL1Q