This marks the first official release of the home console version of Sonic Generations on a Nintendo system, due to the original game not being ported to the Nintendo Wii or Wii U (although a handheld version was produced by Dimps for the Nintendo 3DS). This version of the game features a rewritten script for the cutscenes, now written by longtime Sonic comic writer Ian Flynn.
Both games feature reimagined versions of stages, each with two acts, from past Sonic the Hedgehog games, with Shadow Generations including two stages from games that came out after the original Sonic Generations. In Sonic Generations, each stage's first act is played fully in 2½D as Classic Sonic, while the second acts send Modern Sonic through a mix of 2½D and 3D gameplay. For Shadow Generations, this order is in the opposite, with the first acts being fully 3D while the second acts are 2½D.
Sonic Generation's stages are divided into three eras, each representing a different era of Sonic's career up to 2011.