I expect that it will never come out!
Now that the jokes are out of the way, I can say that I expect it to be a lot of fun. Valve, even though they haven't done a thing for EP. 3 that we know of, are still a very good company. They still make good games, and I expect EP. 3 to be so storied and epic and have a really good plot that will keep me speculating.
What I really want, is a plot where Gordon does not destroy the Borealis. I know Eli told him to, but we all know that Gordon is directly under the thumb of the G-Man and whoever he works for. I feel like it would be a powerful statement to make Gordon, against all of his better judgment, to still do what he's told to by the G-Man.
This could lead into an epic plot-line of rebellion and deception for a Half-Life 3, but maybe I'm expecting too much.