Most compelling non-original - Baldurs Gate. Faerun/Toril is one of the most interesting and complex worlds in fiction, granted it's inherited from the Table Top D&D, but there is so much depth in characters interactions, dialogues, politics, social customs... you can quickly realize by playing for a couple of minutes the universe is rich and vibrant
Most Compelling original - Warcraft. It's as rich and complex as a universe created for videogames can be. Features dimensions, realms, pantheons, diferent cultures, history and civilizations. I'd say when it comes to lore content, it might be the Apex of MMOs







