Valve ported Half-Life to its Source engine as Half-Life: Source in 2004. It was ported to the PlayStation 2 in 2001, along with the multiplayer expansion Decay, and to OS X and Linux in 2013. It was followed by the expansion packs Opposing Force (1999) and Blue Shift (2001), developed by Gearbox Software. By 2008, it had sold more than nine million copies. It is considered one of the most influential FPS games and one of the greatest video games ever made. Half-Life received acclaim for its graphics, gameplay and narrative, and won more than 50 PC ' Game of the Year' awards. The science fiction novelist Marc Laidlaw was hired to craft the plot and assist with design. Valve developed it using GoldSrc, a heavily modified version of the Quake engine, licensed from id Software.

Valve was disappointed with the lack of innovation in the FPS genre, and aimed to create an immersive world rather than a 'shooting gallery.' Unlike other games of the time, the player has almost uninterrupted control of the player character, and the story is told mostly in scripted sequences rather than cutscenes. The gameplay consists of combat, exploration, and puzzle-solving. The player assumes the role of Gordon Freeman, a scientist who must escape the Black Mesa Research Facility after it is invaded by aliens following a disastrous scientific experiment. It was Valve's debut product and the first game in the Half-Life series. Half-Life is a 1998 first-person shooter (FPS) game developed by Valve Corporation and published by Sierra Studios for Microsoft Windows.

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