At a recent Sonic Generations panel during Paris Games Week, Sonic Team's Takashi Iizuka revealed that the original Sonic the Hedgehog will be available in the upcoming nostalgic platformer as a full unlockable game.
Sonic Team also showed off the game's level hub, which is a scrolling selection of doors containing levels and littered with Sonic's furry friends. Don't worry -- their inclusion seems minimal and not too horrific.
Sonic 1 is a cool bonus but it's a shame they couldn't include all the Genesis titles. Of course, by "couldn't" I mean "didn't want to" because SEGA could easily have tossed those in, the cheeky bastards.
[Edit: Jesus fucking Christ that last paragraph was a flippant remark and not intended as a slamming indictment against Sega for fuck's cunting sake.]