Diablo III inhabits a sort of strange hybrid new position in games. Neither entirely single-player nor an MMO, it straddles the world between the two, using its constant internet connection both to connect players to each other in a social experience and to make some cash.
As such, Diablo III finds itself in an unusual position for a game that isn't technically an MMORPG, which is this: players are clamoring for more and better end-game content. Community manager Bashiok acknowledged on the Diablo III official forums that the lack of end-game content is an issue. "We recognize that the item hunt is just not enough for a long-term sustainable end-game," the post admits from the top, and then continues:
Killing enemies and finding items is a lot of fun, and we think we have a lot of the systems surrounding that right, or at least on the right path with a few corrections and tweaks. But honestly Diablo III is not World of Warcraft. We aren't going to be able to pump out tons of new systems and content every couple months. There needs to be something else that keeps people engaged, and we know it's not there right now.
Even though the team is aware of issues around the end-game, though, any significant changes are likely to be quite a way off. The next patch due for the game is 1.0.4, which will contain "as many fixes and changes we can to help you guys out." But PvP arenas aren't due until later patch 1.1, and any larger changes would come even later:
I think both those patches will do a lot to give people things to do, and get them excited about playing, but they're not going to be a real end-game solution, at least not what we would expect out of a proper end-game. We have some ideas for progression systems, but honestly it's a huge feature if we want to try to do it right, and not something we could envision being possible until well after 1.1 which it itself still a ways out.
End game solutions? [Diablo III Forums]