Half-Life 2: Episode One
Released: June 1 2006
Half-Life 2: Episode One continues immediately after the ending of Half-Life 2 without so much as a break for physicist Gordon Freeman. Alyx and Gordon race through City 17 with valuable stolen information, hoping to escape before the Citadel explodes and vaporizes the entire city.
Episode One received high review scores (but not as high as Half-Life 2), sitting in the high 80s. Reviewers were impressed with Alyx's abilities as a companion, the great pacing, and the balance between action and puzzles. The criticisms were the shorter length, the lack of new gameplay elements, and the lighter plot — as part of an intended 3-part episodic game, there's not much more to the plot than escaping the city.
Like its predecessor, Episode One has received minor technical fixes and updates up through 2011, with the most notable being the addition of new achievements.
Alyx is with you for most of the game, and she manages to be a pleasant companion and not annoying at all. You occasionally split up, but frequently the split involves solving a puzzle rather than going on an extended segment alone. At one point she covers you with a sniper rifle as you make your way down a zombie- and Combine-infested street. She very rarely gets in the way, and when she does, she'll happily step aside. Alyx doesn't spout repetitive dialogue and provides some very welcome extra firepower, and you'll rely on it heavily if you're going for The One Free Bullet achievement (where you have to complete the game firing exactly one bullet). Alyx's presence and occasional chatter are a nice change from the usual lone wolf tradition of FPS games.
Changes to City 17
The effects of Gordon's actions in HL2 are very explicit and you see them everywhere you go. The citadel, once cold and imposing, is on the brink of collapse and is incredibly unstable, with a huge fiery storm circling over top. Entire blocks of the city are blasted shells after the open rebellion of the citizens. Combine soldiers are more rare and act independently as a result of cutting off their communications. And with the defence fields down, ant lions and zombies are showing up all over the city. There are no new environments in Episode One, but the environments you're familiar with have changed drastically.
There's a portion early in the game where you're travelling underground. A lot of the time the environment is pitch black, and Alyx can't reliably shoot at anything unless you're lighting it up for her with your flashlight, flares, or burning zombies. The last bit of the underground segment has you hold off swarms of zombies until the parking garage's elevator arrives. It's a crazily intense battle, even after an early patch that reduced the difficulty.
Short & Skinny
Episode 1 is a short game and it's light on story with only a couple of significant plot points and a couple of hints at future additions to the franchise. This might've been a problem at launch when it was more expensive, but now that it's only $8 on Steam, well, who cares. It may be short, but the pacing is great and the variety of gameplay scenarios is quite good.
There's an escort mission late in the game, and like Half-Life 2, the guys you're escorting can be a bit of a pain due to some pathfinding hangups. However, they're much better than in Half-Life 2 overall, so this is only a minor point. Plus, the mission itself is pretty cool: you're leading many small groups of citizens, one at a time, to the train station to evacuate the city. The Combine assault makes some changes to the environment, forcing you to alter your path and tactics with each wave of enemy soldiers. In fact I'm not really sure this should be in the neutral category, but I'm too lazy to move it.
Recommendation: Play it.
If you liked Half-Life 2 you should absolutely follow up with Episode One. If you haven't played HL2, don't bother with the episodes until you have, because you'll have a pretty hard time picking up the story. That said, Episode One is a tight and excellent bit of game which will most definitely be worth the money.