So I got Half-Life 2: Episode 2 over the weekend and I have to say that it was awesome. Gameplay was short, approx. 8 hours, but man it was totally worth it. It went into more details about the story and really helped to build up the other personalities, especially Alyx Vance. If you've been playing HL2, then the ending for Episode 2 will truly shock you.
This is definitely worth playing. If you're new to the Half-Life 2 series, I would definitely suggest you play both the first version and Episode 1 prior to playing Episode 2 to get a better picture of what's happening.