The first sequel to the classic Half-Life 2 takes the form of an episodic chapter in the adventures of Gordon Freeman. It carries on directly from the end of Half-Life 2, with Gordon and Alyx actually going back into the crumbling Citadel to try to stop the reactor from exploding. Half-Life 2: Episode One was first released in 2006.
Initially you only have the Gravity Gun at your disposal and early on it is temporarily changed to a white Gravity Gun by one of the Citadel’s security measures. This alters how it works, allowing you to grab and throw Combine soldiers like the vulnerable ragdolls that they are. From there you must make your way through the Citadel’s dark corridors, solving puzzles and fighting anything that gets in your way. There are plenty of interesting situations from the get-go, like having to catch debris with the Gravity Gun as it rains down on you; having to activate bridges by throwing energy balls at switches; dealing with Stalkers (sinister former humans who have been turned into slaves by the Combine); and the small matter of containing the unstable reactor core (which you get close to and even have to run around as it pulsates at one point, and if it touches you it will kill you).
Eventually you make it out of the Citadel and go on the run from The Combine, as you try to make your way to an evacuation train and out of City 17. There are no vehicles in this episode, but there are escort missions (where you must protect evacuees from Combine attackers), and there’s also a memorable excursion through an enemy-filled hospital. The final battle through the train station – against a persistent and deadly Strider – is also challenging and memorable. And the ending… well, you’ll have to see that for yourself, but it sets up the beginning of Episode Two nicely. Or rather: explosively…
While Half-Life 2: Episode One is undoubtedly a brilliant game, it did receive some criticism for its short length and for its less engaging gameplay, compared to Episode Two. Personally, I think it works well within the overall arc of the Half-Life 2 storyline and is a must play game for Half-Life completists.