Take Baldur's Gate. Ok, you have it in mind now right? A perfect RPG. Now take the world in it, and twist it until almost nothing makes sense. Add a lot of rust and gore and some philosophy and you got Planescape Torment. A world where portals are hidden everywhere and opened by almost anything, where floating talking skulls are a common thing and demons roam free and are a part of society and where YOU are an immortal amnesiac that has to find his soul.