In addition to the mounting concerns about Diablo III's itemization (as I reported previously), players of the game have raised complaints about the game's matchmaking system, which has a strong tendency to queue players into single-man games rather than into parties of 2 or more players.
Blizzard has heard these complaints, and plans to address it. Here's what Bashiok, the game's community manager, said:
This is a known issue due to how the system tries to spread load out over the many game servers. It’s actually doing a great job of putting less strain on the service, but it can result in games with only 2 players. We have some tweaking to do.
As the game's barely been out for a week, it should be no surprise that Blizzard did not have the time (or the ability, really, given the lack of players prior to the game's release) to fully iron out the matchmaking feature. It shouldn't be long before they do, though.