I know the whole "why Half-Life 2: Episode 3 never happened" has been done to death but this article is still pretty interesting. Thanks to Jim Adkins for the link.
Earlier in the interview, Gabe also revealed that there was a lot more content planned aside from the three episodes. "There are three that are in this arc. There are three that are worked out, and those are the ones that we've been talking about so far." This would suggest that after the third episode, there could be another three, followed by additional Half-Life content. Quite what this would entail isn't clear, but as we still haven't had Episode Three, we may never know.
