In an interview with CVG, Valve pledged to make Portal 2 as innovative as the original and not just a quick cash in.
The first game, Valve's Doug Lombardi told us, was just a tester for the ingenious portal system. "We thought we were on to something cool, but we just didn't know for sure because it was radical," he said.
"It could have been one of those things that 20,000 people thought was really cool and everybody else just scratched their heads and thought 'What the hell is this, I don't get it'," added Lombardi.
Of course, the game was huge, which makes a sequel crucial. "Now we've got this challenge of living up to what we did with that.
"People gave it a lot of kudos for being so innovative so, in Valve's tradition, when we hit something, we're not just going to pump out more and cash in on the success of the first one."
Now Valve is determined to impress with the sequel. "We see it as a challenge to really innovate. If Portal was so innovative that it won all these GotY awards, then Portal 2 has to be even more so."
And, Valve being Valve, it's in no hurry. "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.
"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."
So will we get it in 2009? "Perhaps," teases Lombardi. "We're doing a lot of R&D to find out what's going to live up to that promise. 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?"
Let's hope they find that answer soon. Look out for the full interview later this week.