Blizzard acknowledges that Diablo III does not have "a proper end-game," and says it won't for quite awhile to come.
Whether Diablo III is really as much of a mess as its detractors claim, or if it's just a victim of hype and Blizzard's previously unblemished record of success, is a matter of enthusiastic debate. But even Blizzard admits that it's not perfect, and further (and worse), that fans looking for proper end-game content are likely going to have a long wait on their hands.
"We recognize that the item hunt is just not enough for a long-term sustainable end-game. There are still tons of people playing every day and week, and playing a lot, but eventually they're going to run out of stuff to do (if they haven't already)," Community Manager Micah "Bashiok" Whipple wrote on the Diablo III General Discussion forum. "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."
"We're working toward 1.0.4, which we're really trying to pack with as many fixes and changes we can to help you guys out (and we'll have a bunch of articles posted with all the details as we get closer), and we're of course working on 1.1 with PvP arenas. 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," he continued. "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."
Diablo III launched without an end-game, he explained in a separate post, quite simply because Blizzard didn't think it would be needed so quickly. "We believed pre-release that the item hunt would be far more sustainable, and would work to be a proper end-game for quite a while," he wrote. "That didn't turn out to be true, and we recognize that."