Since yesterday, SEGA bought a domain name under soniclostworld.com (IIRC?) and when the new Nintendo Direct went live, the game itself was announced.

Here's the teaser image we got from Nintendo Direct:



The only other interesting news was:
Quote Originally Posted by Sonic Retro
Iwata has revealed that Nintendo & Sega have entered into a “worldwide partnership in the Sonic franchise”, and as such, Sonic: Lost World will be exclusive to Wii U and 3DS owners.
So yeah, this title will probably be skipped by some of us. There isn't any release date announced yet either, so the game's probably still in early development.

Anyways, feel free to state whatever your expectations and opinions are for the game as of right now.