It was Valves debut product and the first game in the Half-Life series.

Players assume the role of Gordon Freeman, a scientist who must escape the Black Mesa Research Facility after it is invaded by aliens.

The core gameplay consists of fighting alien and human enemies with a variety of weapons and solving puzzles.

Valve co-founder Gabe Newell said the team aimed to create an immersive world rather than a shooting gallery.

They built Half-Life using GoldSrc, a heavily modified version of the Quake engine, licensed from id Software.

It won over fifty PC Game of the Year awards and is considered one of the most influential FPS games as well as one of the best video games ever made.

It was followed by the expansion packs Opposing Force (1999) and Blue Shift (2001), developed by Gearbox Software.

It was ported to the PlayStation 2 in 2001, along with another expansion Half-Life: Decay, and to macOS and Linux in 2013.

Valve ported Half-Life to its Source engine in 2004, while a third-party remake, Black Mesa, was released in 2020.

Half-Life 2 was released in 2004, followed by Half-Life 2: Episode One (2006), Episode Two (2007), and Half-Life: Alyx (2020).

Unlike most of its peers at the time, Half-Life used scripted sequences, such as a Vortigaunt ramming down a door, to advance major plot points.

Half-Life has no levels; it instead divides the game into chapters, whose titles flash on the screen as the player moves through the game.

Progress through the world is continuous, except for short pauses for loading.

Some puzzles involve using the environment to kill an enemy, like turning a valve to spray hot steam at their enemies.

There are few bosses in the conventional sense, where the player defeats a superior opponent by direct confrontation.

Instead, such organisms occasionally define chapters, and the player is generally expected to use the terrain, rather than firepower, to kill the boss.

Late in the game, the player receives a long jump module for the HEV suit, which allows the player to increase the horizontal distance and speed of jumps by crouching before jumping.

The player must rely on this ability to navigate various platformer-style jumping puzzles in Xen toward the end of the game.

An array of alien enemies populate the game, including headcrabs, bullsquids, and headcrab zombies.

The player also faces human opponents including the Hazardous Environment Combat Unit (HECU) Marines and black ops assassins.

As part of an experiment, he pushes an unusual material into a machine for analysis.

The spectrometer explodes, creating a resonance cascade that severely damages the facility and opens a portal to another dimension, Xen.

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