Half-Life 2 file extensions

Half-Life 2 (HL2) is a science fiction first-person shooter computer game that is the sequel to Half-Life. It was developed by the Valve Software Corporation and was released on November 16, 2004, following a protracted five-year development cycle during which the game's source code was leaked to the Internet. The game garnered near unanimous positive reviews and received critical acclaim, winning over 35 Game of the Year awards for 2004. Originally available only for Windows-based personal computers, the game has since been ported onto the Xbox and Xbox 360 console, and is also due to be released for the PlayStation 3 in late 2007.

Taking place in and around the fictional City 17, Half-Life 2 follows the scientist Gordon Freeman. Dr. Freeman is thrust into a dystopian environment in which the aftermath of the Black Mesa Incident has come to bear fully upon human society. Freeman is forced to fight against increasingly unfavorable odds in order to survive. In his struggle, he is joined by various allies, including former Black Mesa colleagues, oppressed citizens of City 17, and the Vortigaunts.

The game uses the Source game engine, which includes a heavily modified version of the Havok physics engine. Half-Life 2 has been critically acclaimed for advances in computer animation, sound, narration, computer graphics, artificial intelligence (AI) and physics. As of June 8, 2006, over four million copies of Half-Life 2 have been sold. Exact numbers for digital delivery service Steam and retail have not been revealed, but in general, the former accounts for 25% of Valve's business and is significantly more profitable per unit. Overall, the Half-Life franchise, including Counter-Strike and Day of Defeat, has sold over 20 million units.