Sonic Adventure is the sixth installment in the Sonic the Hedgehog series. Taking place on a fictional island connected to a city, the game follows the adventures of the protagonist Sonic the Hedgehog. An ancient entity named Chaos is released by series villain Doctor Eggman and plots to steal seven Chaos Emeralds for the entity. Sonic is joined by Miles "Tails" Prower, his best friend, Amy Rose, Sonic's love interest, Knuckles the Echidna, who plans to reassemble the Master Emerald, Big the Cat, a cat who attempts to rescue his frog friend, and E-102 Gamma, one of Eggman's robots.
Sonic Adventure received generally positive reviews from critics, who praised the game's graphics, voice acting and soundtrack. The game would later go on to become the best-selling Dreamcast game. A sequel, titled Sonic Adventure 2, was released in 2001 for the Dreamcast.
Sonic Adventure is a platform game in which the player controls six different characters: Sonic the Hedgehog, Miles "Tails" Prower, Knuckles the Echidna, Amy Rose, Big the Cat and E-102 Gamma. They must stop Doctor Eggman from stealing the seven Chaos Emeralds and feeding them to Chaos, a monster known as "the God of Destruction". The first in the Sonic the Hedgehog series to feature free-roaming 3D gameplay, Sonic Adventure is divided into three types of stages: Action Stages, Adventure Fields and Subgames. The division of Action Stages and Adventure Fields was a serious departure from previous Sonic games. There are different goals for each character in the game: Sonic involves high speed gameplay, while Tails must reach the end of the level before Sonic does and Knuckles searches the area for shards of the Master Emerald. Each of the three characters retain many of their trademark moves from previous Sonic games, though they can use updated techniques. Amy must escape from the E-100 Zero robot chasing after her, Gamma shoots through levels to reach a target and Big fishes for his friend, Froggy.
Action Stages are the main playable levels for each character, where the player must face various enemies in order to complete their respective goals. Adventure Fields split up the action, where players can explore the surroundings to advance the plot, discover new levels or search for items which enhance a character's ability (for example, the Light Speed Shoes allow Sonic to run across a path of rings). Subgames deviate from the main gameplay of the character, which include minigames such as kart racing and snowboarding. Players may also find hidden Chao Gardens, which allow them to raise Chao, a sort of virtual pet. Chao can be taken with the player by downloading the minigame Chao Adventure to their VMU, or in the GameCube version, a Game Boy Advance with Sonic Advance or various other Game Boy Advance Sonic games. The player can also raise their stats by giving them small animals that they found by defeating the robots, which improves their performance in Chao Races. There are also eggs hidden throughout the Adventure Fields which can produce special types of Chao.
By playing through Action Stages and Subgames, searching through the Adventure Fields or winning Chao Races, players can earn Emblems. In the case of Action Stages, each one has three Emblems, which can be earned by replaying the stages and fulfilling certain objectives, such as beating the level within a time limit. In Sonic Adventure DX, these can unlock hidden extras such as Game Gear games.