I think its the infinite variety of treasure that keeps people coming back. But I think once you get all of the Uber and bugged items... you've peaked and the game does lose it's appeal like any other game -once you master it there isn't any challenge and you move on to the next new thing. But Diablo can be a lot like gambling - you keep killin meph or pindle hoping you hit the Jackpot and a WF or something falls. But like I said -once you have it all there really isn't much to look forward to. I think there are people who get off on the PK end of it - but you'd think that quake or Unreal would be more satisfying in that respect.