You should be stuck to a board and nailed by a chimp, for teasing us like this.
Either Valve will tell us that it's going to be release in five months time, then when everyone's pre-purchased it within a five hundred thousand kilometer radius of Earth, and the release date is two days away, Valve will go, "whoops, not ready yet" and post-pone the release for a few more months. Probably distract us with some dlc for Portal 2.
Second most probable*: They'll get it finished to a sparkle shine, then drop it on us so they can once in their lives finally go "How's that!"
*hopefully
Or they've skipped Ep3, and just made what they had the first quarter of Half-Life³