User summary and Japanese Wikipedia http://ja.wikipedia.org/wiki/ソニックアドベンチャー:
A 3D action game released in 1998 by Sonic Team for the Dreamcast. The player could choose between six characters and try to clear the different stages, running around in a 3d environment trying to reach the stage goals.
About one year later, Sonic Adventure International was released, with a network ranking applicable to 5 languages. In 2003, a remake of the game was released for the Game Cube, and this version also had a Windows release the same year.
From Amazon: After several years in video game retirement, Sonic the Hedgehog returns as the star of a graphically stunning 3-D adventure game that blows away every other game in the genre. Sonic is joined by five of his friends in a massive quest that spans over 50 game levels filled with remarkable visuals and a pulsating soundtrack. Taking full advantage of the unprecedented processing power of the Dreamcast, Sega's development crew, Sonic Team, has designed several gravity-defying game levels that will keep gamers hooked.