Developed and released to honor the 20th anniversary of the 1991 debut of Sega's star franchise character, Sonic Generations sends past and present versions of the platform hero on a run down memory lane. After an unforeseen incident involving a picnic, a cake, and a hole in the space-time continuum, our modern-day Sonic is transported 20 years into the past where he meets the younger version of himself. Players can choose to play as either version of the character, Modern Sonic or Classic Sonic, throughout the adventure.
The game's levels are inspired by defining stages in the Sonic series' history, including "Seaside Hill" from Sonic Heroes, "City Escape" from Sonic Adventure 2, and "Green Hills" from the original Sonic the Hedgehog. The levels are broken up into three console-era categories: Classic, Dreamcast, and Modern. The style of play in each level is determined by character choice. Classic Sonic's paths play out in the side-scrolling 2D style of the Genesis and Game Gear originals, while Modern Sonic must make his way past both 2D and 3D challenges, as in the more recent Sonic Unleashed for the high-def consoles. ~ T.J. Deci, All Game Guide