The Half-Life universe encompasses everything related to the Half-Life series created by Valve. This includes not just the Half-Life series, but also anything related to Portal, Team Fortress, Counter-Strike, and a couple other releated franchises.
My first foray into Half-Life was from a the original game shortly after the sequel was released. I had heard a lot of fanfare from my friends, so I decided to take a look at the original. Although I didn't play it until years after the original was released, I was still very impressed by the game, enough to continue playing through most of the sequels and expansions.
Unfortunately, it seems Valve is no longer interested in making games, and refuses to outsource their IP to other developers, so the Half-Life series hasn't seen a new release since 2007. Other related franchises haven't seen releases in several years as well.
- Half-Life: Further Data
- Half-Life: Opposing Force
- Half-Life: Uplink
- Half-Life: Blue Shift
- Half-Life 2
- Half-Life: Source
- Half-Life 2: Deathmatch
- Half-Life: Deathmatch - Source
- Half-Life 2: Lost Coast
- Half-Life 2: Episode One
- Half-Life 2: Survivor
- Half-Life 2: Episode Two
The Portal games are meant to take place in the same universe as Half-Life. In Portal, there is a slideshow which shows Aperture Laboratories is competing for contracts against Black Mesa, and the company is mentioned in the ending. Their rivalry is described in more detail in Portal 2 where the CEO of Aperture says that Black Mesa keeps stealing all their technology.
- youtube.com/watch?v=MMggqenxuZc - How Half-Life teaches without a tutorial.