"A lot of R&D" going into Portal 2, says Valve

Speaking to CVG, Valve's Doug Lombardi's assured that Portal 2 won't be simply more of the same, and that the company is investing a lot of time into working out have to take the entire concept forward.

"We're doing a lot of R&D to find out what's going to live up to that promise," he said. "When you think Portal you think about really innovative gameplay, clever writing and really dark humour. So how do we take that and follow up upon that idea, rather than just cashing in on it?"

Don't hold your breath on a quick release, however.

"We could have quickly put out Half Life 2 in 18 months. It would have been on the same engine and been a reverse run through Black Mesa. But that's not our style," Lombardi added.

"I don't think it'll be six years until you see the next Portal, but it will definitely not just be seeing Portal with different coloured textures."

More through the link.