A select excerpt from Eurogamer:

"In typical Valve tradition, it won't be Portal with different colours," said Lombardi, dressed as a companion cube. "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.'