If you found science-fiction author and former Valve writer Marc Laidlaw's synopsis of Half-Life 2: Episode 3 interesting to read, you might find it interesting to play, kinda, sorta. Laidlaw recently published a gender-swapped, name-changed fan-fictionesque version of the possible major events of the never-published episode of Half-Life 2 called Epistle 3, which created a bit of excitement among Half-Life 2 fans and also spawned a game jam using Laidlaw's story as its inspiration.
There are a number of games already submitted to the jam, and I just played one made by Blendo Games, maker of Quadrilateral Cowboy and Thirty Flights of Loving. It's a Half-Life 2 mod called Tiger Team. It's only a few minutes long, and it takes you through some of the events, kinda, of Laidlaw's story, sorta. (Here's a version of the story with the game's real character names which I found easier to follow.)
I'm not honestly sure I knew what was going on with everything in the mod—there's a lot of bouncing around between scenes, and without having read the story I wouldn't have been able to follow a damn thing going on. But if you read the story and then play the mod, you should be able to grasp most of what you see. Besides, since we'll never get to play the real thing, this may be as close as we can get.
You can download the Tiger Team mod here.