Valve is marked for its consistent quality, but not its consistent scheduling. The PC powerhouse is notorious for unpredictable releases and lengthy delays, but the developer/publisher claims that it isn't schizophrenic, and defends its spotty launch dates.

"I think it's fair to say that Valve never approaches a product release the same way twice," says Valve marketing chief Doug Lombardi. "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."

When will market conditions be right for Episode Three? Just askin' ...

Valve: 'We're not schizophrenic' [CVG via Xbox World 360 magazine]