Maybe it’s the seamless integration of familiar adventure-game elements (loathsome demons, valorous heroes, creepy dungeons). Maybe the polished 3-D graphics. Or maybe the curiously satisfying thrill of crushing a hellspawn’s skull with your battle-ax. (Myst this ain’t.) Whatever it is, this addictive game, Diablo, has something that lifts it magical helm and shoulders above the rest of the typical sword-and-sorcery fare. A