I basically wanted to write this post, so I will pull the old " ^ What he said ^ "Valve
First off they're finally going to move to a new engine, so I'm curious how that's going to turn out. Like, do they want cutting edge stuff, new technology or will they be content with some stock next-gen features and modest requirements so most of their userbase can run it. Personally haven't thought for a while they're going to duke it out with the big guns (Crytek, Epic, Dice, ND etc) in the tech department with Source 2, but have huge expectations regarding animations and maybe physics. We'll see.
Also, new IP. Haven't done an original new game since L4D, so want to see if they can come up with something defining again. Wouldn't mind if they start up that space pirate sim project again or F-Stop.
And Half-Life 3. There's lots of expectations regarding that game. Can they live up to it? (probably not. who could?). But I think for a lot of people they have to prove themselves with that one.