It's the first Sonic the Hedgehog game of the current generation of consoles, technically, and it's bringing Sonic up-to-date, Super Mario Galaxy style. Sega may be calling it Sonic Lost World, but to me it'll always be Super Sonic the Hedgehog Galaxy.
It's a good thing this is exclusive to Nintendo consoles, because we wouldn't want to get that SMG funk all over the PlayStation 4 or the Xbox One. No, this is has Nintendo written all over it, from its color-coded new villains (The Deadly Six, because Sinister Six was taken) to the self-contained floating levels to the inclusion of Color Powers, a carry over from Sonic Colors (Sonic Colours in Europe) that could, if you squint real hard, be compared to Mario suits.
It's a pretty game, but then no one ever accused the franchise of being ugly.
Super Sonic the Hedgehog Galaxy will be out later this year for the 3DS and Wii U. In case you missed the trailer, you can see it here. Looking for 3DS shots? Squint your eyes until these look all pixelated.