No matter how hard it tries, Sega can't seem to nail a modern Sonic game at least, nothing has managed to match the affection we still hold for the '90s platformers. I'd argue that Sonic Generations was pretty decent, but overall, Sonic games are pretty average nowadays. There's no point sugarcoating it.
Sonic Utopia is a fan made game which imagines Sonic in an open world setting. As the video below demonstrates, it's more high-speed parkour than platformer, coming across like a meeting between SSX and Yooka Laylee. According to its creator Mr Lange, Utopia is "an experiment that not only tries to expand on Sonic gameplay in an intuitive way in 3D, but also aims to capture the best of Sonic's style and tie it together in a cohesive experience."
Although the game is still in a "raw state" you can download the demo and give it a go (be warned though: the Dropbox account is getting pummelled, there's an alternative direct download here).
I don't know what Sega will make of this, but optimistically, it'd be cool if this guy got a job making a halfway-decent official Sonic game. Imagine that?