I just finished it and overall it was an excellent game. My only complaints are the stuttering that I encountered a bunch of times throughout the game and the way they left me hanging at the end without an explanation. They build up the story throughout the game and they don't even wrap it up which would be nice if half life 3 was coming out next year but I suspect it won't be coming out for quite a while. Some sort of weird twilight zone type ending left me feeling that the game was incomplete. Other then those 2 complaints the game was great.
How much memory do you have? If it is only 512, that might cause some of your stuttering. I hated that idea, as I remember when 512 was a lot, but I recently upgraded to 1gb after huge stutter problems in Battlefield 2. It runs like a charm now. I should go back to HL2 and see how that runs now.
As far as when HL3 will come out, I don't hold out too much hope but, supposedly it won't be as long as the other 2 games too. They say they just going to use the same engine they used on HL2 so that they don't have to spend so much time making an engine and tools, only to start all over with a new game, having to make and learn new tools. I know they say that now, but who knows. Still, hopefully it won't take as long to make.