The cliffhanger ending of Half-Life 2 felt like the dark middle arc of a trilogy, and left us with more questions than answers. The Half-Life 2: Episode One (formerly Aftermath) expansion promises to answer some of those questions ... but will raise even more.
Episode One centers entirely on the now-doomed City 17. Thanks to Gordon Freeman, the annihilation of those oppressive rulers, the Citadel, has now put everyone still inside the city in peril. The action focuses around the characters you wished you spent more time with in Half-Life 2, namely Alyx and Dog. We'll have to assume they've learned new tricks and have new ways of interacting with the Half-Life world. But take heed: the Citadel's aliens co-horts, the Combine, haven't exactly been catching up on their knitting while you were away, either.
This past summer, the Lost Coast tech demo gave us a taste of what new technological kick-sauce is in store for Gordon's friends. (If you already own Half-Life, Lost Coast is free via the Steam direct-download service.) It was only a short adventure, but it showed off amazing High Dynamic Range lighting technology that left us breathless. HDR lighting models the way we naturally see light. You know that blindness thing that happens when you look straight at the sun? Your iris closes, and it's harder to see into shadows. That's just what HDR lighting does, and it will be all over the Episode One expansion. While this is heavy-duty lifting for your computer (only a top-drawer rig will run HDR properly), it's a subtle effect. By clever use of tools like these, the developers at Valve have fashioned an effective method of telling the story through gameplay. This only makes their hyper-realistic hog pile, the Half-Life 2 engine, even more immersive.