After blowing up the nuclear reactor, everything freezes in place.  Out of the thin air, the same spooky agent appears that you saw at the end of the first Half-Life.  He begins by finishing the sentence that your partner was saying, "...time.  Do we really have time Gordon?" he asks.  He continue to tell you that there are once again chooses that must be made to determine what Gordon's future holds.  However, he says, this time he won't leave the decision up to free-choice.  He says that he will make the decision for Gordon.  He ends by saying that his time here is up, and he walks through a door of white light.  The credits role.