Blizzard must have built Diablo 3 for the long haul. Their previous game, Diablo 2, has been on store shelves for ten years. Blizzard bolted a real money auction house to Diablo 3, slaving all the game’s code and much of the player experience to feed this cash cow. So why isn’t there anything in Diablo 3 that would make a player want to keep playing after the final boss coughs out his last breath? Check out this article that explores the problems Diablo 3 has with designing for long-term play. Joystiq has the story.
Diablo 2 had a high level cap, character points to play with and allocate, tons of loot with strange effects to chase and build characters around, PVP, and gear upgrade paths through gems and runes. In short, there never was an endgame, there was always some new rabbit to chase.
Diablo 3 has a much simpler character system, builds are mostly a thing of the past, there’s no PVP, and upgrade paths are minimal at best. It’s a shame.