Planescape Torment is the ultimate role-playing game that uses the D&D system -- a great balance of combat, quest-fulfilling, and most of all, storytelling.  I played the old Pool of Radiance game, Baldurs Gate, and Icewind Dale.  Planescape: Torment is better than them all.  But the game is not just a great D&D game.  It is a great role-playing and adventure game.  Every character trait matters.  Higher intelligence gives you access to more dialog options.  Higher wisdom allows you to accumulate memories and experience faster.  It is very rare to find a game that puts this kind of value on intellectual traits.