Episode Two offers the best Half-Life 2 experience thus far.
Episode Two comes after another 15 months from Episode One, but this one is actually worth it. It's lengthier, it advances the story while also setting the stage nicely for the next installment, it introduces some new stuff, and is very well paced. On the other hand, it's still on the short side considering how much we needed to wait for this one as well.
So, Episode Two picks up right after the previous installment. You wake up in a train wreck after narrowly escaping City 17. From here you team up with Alyx once more and try to make your way to White Forest, a base of the human resistance. A lot of things will happen throughout this journey, both in terms of story, as well as action.
The best thing about the campaign is the pacing. It has a nice build-up, and when it reaches optimal cruising speed it sticks to it, unlike the original HL2, which would often times cut the action just when things were getting interesting, or make a rather noticeable shift from a fast-paced mission to a slow mission. So kudos to Valve for making the action feel more continuous, basically less fractured.
Like I mentioned earlier, there's also some new stuff in this one. My choices for best new stuff would be the Combine Hunter (which is a mean and agile tripod unit, kind of like a small Strider) and the sticky bombs. Your encounters with Hunters are sure to get hectic, specially when you've got a pack of them charging you. And using sticky bombs to take down Striders is pretty awesome. Now combine the two and you've got one hell of a fight.
Basically, the only major interruptions to the action are story moments, which are well executed for the most part, though the story still doesn't make a whole lot of sense. There are quite a few things that the upcoming Episode Three needs to explain. But we'll have to wait for that one a while longer, since it isn't coming this year for sure.
For me, this is the first HL2 game from which I walked away satisfied. So unlike Episode One, I'd actually recommend this one. You can purchase it as part of the Orange Box if you haven't played anything HL2 so far, or get it separately for about $12 from Steam (12 euros in the E.U. - someone should tell Valve that it's not exactly the same thing). For that price it's worth it.