'This is not World of Warcraft, we aren't going to be able to add new content every couple of months', says dev

There are not enough features for a long-term sustainable end-game in Diablo III, Blizzard's community manager has admitted.
Speaking on the official forum, Bashiok said that whilst there was still a lot for players to do, such as an item hunt, he recognised that users would run out of things to do.

He claimed that Blizzard were currently working on the issue, although it wouldn’t be resolved for some time, and also warned users not to expect the same amount of new content that World of Warcraft receives.
“We recognise that the item hunt is just not enough for a long-term sustainable end-game,” said Bashiok.
“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). 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.