Takashi Iizuka the producer of Sonic Generations has revealed that the original Sega Mega Drive/Genesis Sonic the Hedgehog game will be an unlockable title. He hasn't explained how to unlock the game but it is a nice surprise to hear it been included. If you haven't brought the classic game then this could save you some points.
Sonic Generations will features both Modern and Classic Sonic and Tails while they battle against villains such as Shadow the Hedgehog, Metal Sonic and others. The game will be available November 1st in the US, November 3rd in Australia and November 4th in Europe. If you still on the bench about preordering the game, have a go on the demo which is on Xbox Live Marketplace.