Half-Life

Half-Life is an FPS developed by Valve Software and published by Sierra On-Line, released in 1998.

Plot
Young scientist Gordon Freeman works at the Black Mesa Research Facility in New Mexico. He is part of an experiment that goes horribly wrong, opening portals to a parallel universe. Soon the base is packed with hostile and deadly creatures. To make matters worse, the government decides to cover up the incident by sending the marines to kill not only the aliens, but all witnessess. Freeman ultimately finds that Black Mesa had been experimenting with teletransportation to the alien world, to which he must travel to slay the creature keeping the rift open.

Development
Half-Life was the first game by Valve, a company founded by former Microsoft employees Mike Harrington and Gabe Newell. It runs on the GoldSrc engine, a heavily modified version of id Software's Quake engine. Although originally slated for a late 1997 release, and the game was technically completed in time, the team realized that it was just not fun to play. Consequently they took another year to revamp the design and writing.

Reception
Half-Life was a massive success, both critically and commercially. It was particularly praised for its immersion: unlike most FPS at the time, the camera is always Freeman's point of view, and the game never stops for cutscenes or text expositions during which the player is not in control of him.

Expansions
Gearbox Software produced three official expansions:
 * Opposing Force (1999), in which the player takes the role of a marine in the cover-up.
 * Blue Shift (2001), in which the protagonist is one of Black Mesa's security guards. It was originally part of the cancelled Sega Dreamcast port, and later received a PC release.
 * Decay (2001), in which two players play co-op as two female scientists. This expansion is exclusive to the PlayStation 2 version, although there is a fan-made PC port.

Also, a multitude of official and unofficial mods was released for it, such as Natural Selection, Day of Defeat, Team Fortress Classic, and Counter-Strike.

Sequels
Half-Life 2 was released in 2004, with episodic sequels in 2006 and 2007. After a long hiatus, virtual reality game Half-Life: Alyx was released in 2020, rekindling hopes and rumors for a future Half-Life 3 to conclude the story.

Re-releases
The game was ported to its sequel's more advanced engine in 2004, as Half-Life: Source. However, this version was criticized for being very glitchy, but otherwise nearly identical to the original release. A team of fans decided to produce a proper remake that fully used the new engine's graphics prowess and greatly expanded on the original level design. This version, called Black Mesa, was finally completed and commercially released with Valve's permission in 2020.