Doug Lombardi, vice president of marketing at Valve, has said that Portal 2 won’t be teleported to a computer or console near you in 2008. To quote him:
“In typical Valve tradition, it won’t be Portal with different colours. I think that when you hit something like that, you have two choices: you can quickly replicate it and stick it out there — do the opportunistic thing and cash in on it; or you can do the crazy thing like we did after Half-Life was so successful and go off and try and say, ‘Okay, that was revolutionary, so its successor has to be equally as revolutionary.’
That’s the spirit I think we’re approaching it in. You won’t see a new Portal at retail this Christmas because of that. That’s the trade off. People want more, but we don’t want to give them more of the same right away because that would just be boring.”
According to Eurogamer the original game (described as an “experiment”) went very well, then, and now developer Valve is doing plenty of research and development to find out what “more” it is going to offer.