Half-Life 2: Episode One is the first of a series of stand-alone episodes based on the acclaimed shooter epic. —Mac World The setting for most of your previous adventures is nothing more than a smouldering scar on Episode Two's skyline and the Citadel looks like a long-finished game of girder-Jenga. Episode Two feels wild, dangerous and cool. Half-Life 2: Episode One continues the single-player story from the critically acclaimed Half-Life 2. Players slip on the battered spectacles of Dr. Gordon Freeman to engage in more alien and mutant battles from within the decaying walls of City 17.

Half-Life 2: Episode One is the follow up to the original Half-Life 2, featuring pretty-looking HDR effects, more cooperation with Alyx, more physics puzzles and red skies.

Episode One was the first in a planned trilogy of shorter episodic games that continue the story of Half-Life 2 (2004). Valve wanted to release new games quickly, without spending years developing a major new product with new tools. For Episode One, they focused on the player's relationship with Alyx, developing her artificial intelligence. Half-Life 2 Episode One Half-Life 2 Episode 1 - Part 8 - Haunted Hospital Hallways (00:18:42) Jan 21 2015: Half-Life 2 Episode One Half-Life 2 Episode 1 - Part 9 - To the Trains (00:10:14) Jan 21 2015.

It also adds some Hunters. Woo.

Vortex Hopwire Grenade

This 'weapon', also nicknamed the Black Hole Grenade, can be spawned through the console. It is very powerful, drawing everything nearby into it before collapsing and killing enemies instantly. However, it is glitchy and has an unfinished model; it re-uses the Rollermine model. According to Episode Two's commentary track, this would later become the Magnusson Device.

If used too close to Alyx, it can kill her and spawn endless ragdoll copies, and often crashes the game to desktop.

Unused Models

models/props_outland/pumpkin01_explosive.mdl contains an untextured pumpkin from an early build of Episode Two.

Unused G-Man Dialogue

There are various soundscripts located in Half-Life 2: Episode One that are pre-loaded, but whose respective sound files were omitted in versions after the preload release. The G-Man is one example of this. Here are various lines from the intro, and his only appearance in the game since the Vortigaunts hinder him from getting to talk to Gordon. Seemingly, he was to speak with Gordon in early revisions before being cut off, whereas in the final he is instead stopped from even initiating conversation.

Oh no, Freeman, come back. Come back here, now.

Get back here.

laughter

Oh! Not for long.

Not this time.

Snarling

Well...well shit.

So nice to have you with us, Mr. Freeman.

Get back where you belong, and forget about all this until-

We meet-

Again.

Again.

Unused Alyx Dialogue

Unlike the fucking soldiers who volunteer for what they get.

Alyx has a small number of unused pieces of dialogue involving the Stalker train that she and Gordon ride to get out of the Citadel, where she expresses fear for the Stalkers. As Bill Fletcher mentions in the developer commentary, her reactions to the Stalkers went through a number of iterations. In very early versions, Alyx was frightened by the Stalkers. This didn't work since it clashed with her earlier reactions to Stalkers in the Citadel. In the second revision, Alyx expressed anger at the Stalkers' predicament. Fletcher mentions early versions of this new idea didn't work out since Alyx's transition from generally upbeat to blind rage was too sudden. Ultimately, through 'rewrites and rigorous testing', the team found the right tone for the scene - a simmering anger level that was more in tune with the situation.

In addition to this line also being removed in releases after the preload version, it is located among the closed captions, its string is blanked out however. By comparison, the earliest iteration of Alyx's Stalker train-related dialogue is still present in the game's files.

Unused Barney Calhoun Voice Clips

The best thing you can do is run defense.

Ammo's in short supply; a lot of the citizens are unarmed at this point.
Barney was originally meant to say these lines when Alyx and Gordon meet up with him at a Resistance safehouse in the Urban Flight chapter.

Okay then. You take care of yourselves. I'll see you out there.
Barney was meant to say this when Alyx and Gordon are about to leave the Resistance safehouse.

Dr. K's in fine fettle, isn't he?
Barney was supposed to comment on either Alyx or Gordon about Isaac Kleiner's condition either during the Urban Flight or Exit 17 chapters.

Oh, you're kidding me. A Strider? In here?

Okay, where the hell did that strider come from? I thought they'd all hightailed it out of town by now.

Hey, see if you can bring that strider to its knees, buddy.

Good job knee-capping that strider!
Meant to be used for a Combine Strider battle in the first section of the Exit 17 chapter.

Are you crazy? Er, well, don't answer that.
Barney was supposed to say this if Gordon was to interact with him when under fire with a tough enemy entity during the first section of the Exit 17 chapter.

Half-life 2: Episode One For Mac Torrent

A gunship! Well this is one hell of a wrinkle.

That's one less gunship in the world!
Lines for a Combine Gunship battle in the Exit 17 chapter.

Okay, we've gotta take out that armored personnel carrier or no one will be able to get through.
Barney was supposed to say this when encountering a Combine A.P.C. during the Exit 17 chapter.

Oh hell, it looks like that soldier found himself a rocket launcher.
Barney was supposed to say this when spotting an Overwatch Soldier equipping a Rocket Propelled Grenade.

Oh well...I don't have a trophy room anyway.
Barney was to say this if Gordon managed to defeat a tough hostile entity during the Exit 17 chapter.

Good. Now, to catch up on those beating quotas.

Half Life 2 Episode One Walkthrough