Aside from making and supporting quality games like Team Fortress 2 and Left 4 Dead, Valve is notorious for their bizzare release schedules: the sequel to Half-Life took six years to be released yet Left 4 Dead received its follow-up within a year. Half-Life 2: Episode Three? Hardly anything is known about it. Portal 2, on the other hand, is going on sale in just over three years since the release of Portal.
Valve marketing director Doug Lombardi offers an explanation of these release patterns as Valve simply trying to put out the best game they possibly can:
"I think it's fair to say that Valve never approaches a product release the same way twice. With Half-Life 2 we took six years to create an epic sequel, then we immediately shifted to episodic releases, which were then followed by the release of a new IP (Left 4 Dead) which was given a sequel in less than a year. Now, with Portal 2, we've taken a couple of years to produce a full sequel to a game that was launched in episodic size. The point is not that we're schizophrenic, but that we try to productise every game in a way that's best for it, given market conditions and other factors."
It's not a bad thing to focus on quality but if you're going to take a really long while to put out something like Episode Three, it wouldn't hurt to drop a few details on what you're working on. We're more than ready to get rid of the Combine once and for all.