Eternal Darkness: Sanity's Requiem

One of the very few M rated GameCube games.. and, as far as I know, has a unique core sanity mechanic that fairly routinely breaks the fourth wall, aimed at driving you, the player, at losing your own sanity, not merely depicting this happening to your character.

Also, IIRC, the first iteration of Pikmin, a genuienly novel kind of game. Luigi's Mansion, also a pretty unique kind of game.

Oh, and they remade Metal Gear Solid on it, with better graphics than the PS1.