Sonic Team sought to re-imagine the most popular aspects of the franchise in high-definition, and developed the game using the Hedgehog Engine.

The Windows version is noted for its active modding scene, where a dedicated community creates new gameplay mechanics, levels, and assets for the game.

Reception to the 3DS version was mixed; reviewers criticized its short length and design, and deemed it worse than Dimps' previous Sonic games.

Both Sonics collect rings as a form of health,[6] and power-ups such as elemental shields, invincibility, speed shoes, skateboards, or Wisps.

[16] In the console version, once the game has been completed, both Sonics can transform into their super forms by collecting 50 rings in a normal level.

The concept art, as well as cutscenes and character profiles, can be viewed in a Collection Room, while music can be set to play in any level, mission, or boss.

Modern Sonic awakens in White Space and rescues Tails after traveling through Green Hill.

Modern Sonic and Tails eventually meet their Classic counterparts, and form an alliance to restore their world.

They rescue many of their friends, including Knuckles, Amy, Rouge, Cream, Blaze, and the Chaotix, while battling old enemies for the Chaos Emeralds.

However, the two Sonics use the Chaos Emeralds to transform into their super forms and defeat the Time Eater, restoring the timeline to normal.

[30] The team chose to develop on the high-definition (HD) PlayStation 3 and Xbox 360 consoles, wanting the game to re-imagine levels and aspects of previous entries with high-quality graphics.

[30] According to Iizuka, one of the hardest parts of developing Generations was adapting 3D levels to 2D, since their "defining" elements and themes were designed to specifically work in 3D.

[34] The team faced bigger difficulties developing on the 3DS; Iizuka claimed they were unfamiliar with the system's capabilities and limitations.

[37] In contrast to the casual-oriented Colors,[38] Sonic Generations was designed to appeal to the series' core audience.

[39] Sonic Team also created a new character: the Time Eater, who serves as the game's main antagonist.

[31] The musical score of Sonic Generations was primarily composed and arranged by Jun Senoue, with contributions by Richard Jacques, Naofumi Hataya, Hideki Naganuma, Kenichi Tokoi, Tomoya Ohtani, Crush 40, Circuit Freq, and Cash Cash.

[47] It was initially announced for the PlayStation 3 and Xbox 360; the 3DS and Windows versions were leaked in a Sega Sammy Holdings financial earnings report.

[59] A pinball minigame based upon Sonic the Hedgehog 2's Casino Night level was released as downloadable content for the Steam version of the game on December 26, 2011.

Nathan Meunier of GameSpot called the graphics arguably the best of the series, praising the detail put into recreating each level;[6] this statement was echoed by Tim Turi of Game Informer.

[22] Jack DeVries and Brian Altano of IGN offered similar praise for the visuals, and described its remixed tracks as "cool" and its sound effects as "spot on".

[14] DeVries and Altano considered the "classic"-style gameplay to be a successful revival of the 1990s Sonic games and the "modern"-style to be similarly enjoyable, though they offered minor criticism of the former's floaty physics and the latter's reliance on speed.

[9] Famitsu favorably compared the sense of speed to that of racing games and praised the "nimble" camerawork, describing the overall experience as addictive.

[14] Bramwell felt that Generations still suffered from problems present in prior games, and found its controls laggy and criticized certain segments requiring split-second precision.

[10] Several reviewers pointed out the fact that there are little difference between the gameplay of classic and modern Sonic, since both are limited to 2D movement.

[74][10][2] James Newton of Nintendo Life described it as "short and unambitious" and compared it unfavorably to the then-recently released Super Mario 3D Land.

[2] Dan Whitehead of Eurogamer agreed, criticizing the handheld game's lack of variety, replay value, and inconsistent design and calling its levels "a pain to explore", though he offered praise for its visuals and recreations of classic Sonic moments.

[89] An update to the Xbox 360 version in November 2021 added support for 4K visuals and an increased frame rate when played on Series X/S.