To celebrate the 20th anniversary of Half-Life 2 Valve has released a ton of new content for the game as well as releasing it for free in it's entirety for a limited time! There is also a Half-Life 2 documentary that I've embedded here for you to view, I haven't seen it yet but plan to watch it as soon as I can. Seems like if you haven't played Half-life 2 yet or wanted to get back in, now is a great time.

Some of the changes in the new version:

* Episodes One and Two are in the box. Half-Life 2 now includes the complete Episode One and Episode Two expansions along with the base game. They’re accessible from the main menu, and you will automatically advance to the next expansion after completing each one.
* Developers Commentary for Half-Life 2. While the Episodes have always had commentary tracks, the base game never did... until now. We got the team back to record three and a half hours of new behind-the-scenes commentary for Half-Life 2.
* Integrated Steam Workshop support. Browse, install, and play user-created content for Half-Life 2 without ever leaving the game. Look for it in the Extras menu!
* Bug fixes and new graphics options. Visual pops, missing sprites, and mismatched lighting introduced in updates over the years have been scrubbed away. And we've added some settings to push the visual fidelity of Half-Life 2 farther than was allowed in the original release.

https://www.half-life.com/en/halflife2/20th
https://store.steampowered.com/app/220/HalfLife_2/