If you're looking for an RPG worthy enough to be played on your GameCube, then Tales of Symphonia is the one to have.
ToS is the story of Lloyd, his friend Genis, their teacher (and Genis' sister) Raine, and their friend Collete who's been picked at The Chosen of Mana who partake in a pilgrimage to regenrate the decaying world of Sylvarant. Along the way, they encounter various allies and adversaries, especially the evil Desians (evil half-elves) who enslave humans and have a grudge against Lloyd after he makes a scene at one of the ranches.
If you love RPGs, own a GameCube and are looking for a game to play with, then ToS is the game to own!