Sonic Adventure is an instant Dreamcast classic that shouldn't be missed by any Dreamcast owner.  The game features Sonic in full 3d with newly detailed level enviroment.  This was one of the first games to launch with the Dreamcast and is still one of my favorite Dreamcast game.  The game features a brand new system called the "Chao system" you basicly take care of them and show them new moves it's very simple but you'll need to have a VMU card to do it.  The game features more then 5 playable characters.  The story in the game is very lame if you ask me they could have done better, not to mention the english dubbing is terrible so just stick to japanes language and english subtitles.