As the teaser suggested, Generations will feature playable versions of both the modern "green eyed" Sonic and the pot-bellied 1991 incarnation. It's set across Sonic's three defining "eras" and features reimagined classic environments that will come in 2D or 3D flavors.
Each Sonic has his own special moves -- Classic Sonic will have the Spin Dash and Spin Attack while modern Sonic will have his Homing Attack and Sonic Boost. SEGA also promises an interactive menu for "complete immersion" and a number of bonuses and popular characters that are revealed throughout the course of the game.
The game's story is about a number of "time holes" created by a "strange new enemy". Through these holes, Sonic encounters a number of past characters, including Classic Sonic, and they team up to save the universe.
So that's a thing. Excited? Skeptical? All I have to say right now is this better feature Chemical Plant Zone or it can GTFO!