Sonic Adventure 2

Sonic Adventure 2 is a 3D platform game divided into two campaigns: Hero and Dark. In the Hero campaign, players control Sonic, Tails, and Knuckles, who fight to save the world; in the Dark campaign, players control Shadow the Hedgehog, Doctor Eggman and Rouge the Bat, fighting to conquer it. Each campaign cycles through levels of its three characters, telling different sides of the story. Levels have a variety of themes (such as cities, jungles, desert pyramids and outer space), with some followed by boss fights. The two campaigns' stories occur in parallel; completing both campaigns unlocks a final story with all six characters, culminating in a final boss fight.

Sonic and Shadow's levels are fast-paced and emphasize platforming. Their homing attack can lock on to robots created by Eggman and GUN, and they can grind on rails. Tails's and Eggman's levels are slower and oriented towards multidirectional shooting; they are confined to mechs in which they can jump short heights, hover and shoot enemies. Knuckles's and Rouge's levels feature open exploration with treasure hunting; in each level, they must find three shards of the Master Emerald.

Doctor Eggman learns of a secret weapon from the diary of his deceased grandfather, Professor Gerald Robotnik, and infiltrates a high-security Guardian Units of Nations (GUN) facility to revive it with a Chaos Emerald. The weapon—Shadow, a black hedgehog who proclaims himself the "Ultimate Lifeform"—offers to help Eggman conquer the world, telling him to rendezvous at an abandoned space colony, the ARK, with more Chaos Emeralds. Shadow has vowed to fulfill a promise he made to his friend, Eggman's cousin Maria, before she died; the amnesiac Shadow interprets the promise as one of revenge. Shadow steals a Chaos Emerald, and GUN arrests Sonic after mistaking him for Shadow.

Knuckles encounters Eggman and Rouge, a government spy, attempting to steal the Master Emerald. He stops them by shattering it and searches for the scattered shards to repair it. Rouge follows Eggman to the ARK, where Shadow shows Eggman the Eclipse Cannon, another weapon created by Gerald. Shadow plans to charge the cannon with the seven Chaos Emeralds and use it to take over the world.

Sonic Adventure, the first 3D platformer in Sega's Sonic the Hedgehog franchise, was developed by Sonic Team and released for the Dreamcast in Japan in 1998. Although the game was a critical and commercial success, Dreamcast sales struggled to meet Sega's expectations. The Adventure team was downsized, and Sega relocated Adventure's director, Takashi Iizuka, to San Francisco, California, to establish Sonic Team USA. Sega wanted to repeat the pattern of developing a game in Japan and its sequel in the US as it had done with the original Sonic and Sonic the Hedgehog 2 (1992). Only 11 staff members—significantly smaller than Adventure's team of 120—joined Iizuka, and they began working on Sonic Adventure 2 after they spent six months localizing Adventure for the West.

Shiro Maekawa, who wrote portions of Sega's Panzer Dragoon Saga (1998) and joined Sonic Team during Adventure's production, conceived and wrote Adventure 2's story. Maekawa accepted the role after he learned that he did not need to be an artist to create a story or storyboards. Because Adventure 2 would be the first Sonic game released during the 21st century, Maekawa wanted a substantial portion of the story to take place in space. The rest of Sonic Team was apprehensive, but Maekawa convinced them.

Sonic Adventure 2 received "generally favorable" reviews. Critics appreciated its multiple playing styles. According to Edge and Four-Eyed Dragon of GamePro, the three styles and bonus features such as Chao gardens were engaging. Johnny Liu of GameRevolution praised its replay value of multiple playing styles and 180 different goals.

Anthony Chau of IGN called it one of the best Sonic games: "If this is the last Sonic game in these declining Dreamcast years, it's satisfying to know that the DC didn't go out with a bang, but with a sonic boom." In 2022, IGN named it one of the best Dreamcast games.

Sonic Adventure 2 is frequently ranked among the best Sonic games. GameSpot and Kotaku deemed it a satisfying conclusion to Sonic's run on Sega hardware, and Game Informer considered it a worthy sequel to Adventure. However, journalists have characterized Adventure 2 as divisive, and the 2012 rerelease received "mixed or average reviews" according to Metacritic. Some fans regard Adventure 2 as the franchise's pinnacle, but others find it unfocused—"a jack of all trades, master of none", as The Escapist wrote. According to The Escapist, "depending on who you ask, [it] represent[s] the franchise at its best and at its worst."

Common elements of retrospective praise include Sonic and Shadow's levels, the Chao Garden, and the soundtrack. GamesRadar+ felt Adventure 2's increased speed and emphasis on spectacle positively influenced the series. Conversely, its focus on multiple characters with different gameplay styles has been divisive. While IGN praised the gameplay variety, Kotaku noted that many only like the Sonic and Shadow levels; retrospective reviewers have criticized the other characters as frustrating and cumbersome.