Sonic Heroes is a 2003 3D platform game developed by Sonic Team USA and published by Sega as part of the Sonic the Hedgehog series. The player races a team of series characters through levels to amass rings, defeat robots, and collect the seven Chaos Emeralds needed to defeat Doctor Eggman. Within each level, the player switches between the team's three characters, who each have unique abilities, to overcome obstacles. Sonic Heroes abandons the action-adventure and exploration-based gameplay of its predecessors Sonic Adventure (1998) and Sonic Adventure 2 (2001) and instead returns to the linear style of Sega Genesis-era Sonic games. The game was the first multi-platform Sonic game, produced for the GameCube, PlayStation 2, Xbox, and Windows platforms. Sonic Team USA's Yuji Naka and Takashi Iizuka led the game's 20-month development. The team wanted Sonic Heroes to appeal beyond Sonic series fans and so designed a game that did not depend on the continuation of its predecessors. The team revived elements not seen since the Genesis Sonic games, such as special stages and the Chaotix characters. Sega released Sonic Heroes in Japan in December 2003 and worldwide in early 2004. Reviewers were polarized. They praised the game's focus on fast gameplay and noted its similarities to the series' original 2D entries, a choice that some considered an improvement from the Sonic Adventure games. Reviewers also highlighted its graphic design and detailed environments and textures. Critics, however, derided the game for not addressing the problems of previous series games, such as poor camera, controls and voice acting. Despite mixed reviews, the game was commercially successful, with 3.41 million copies sold by 2007.