It was followed by two episodic sequels: Episode One (2006) and Episode Two (2007).
Like its predecessor, Half-Life 2 is a single-player first-person shooter broken into several chapters, permanently casting the player as protagonist Gordon Freeman.
Despite the game's mainly linear nature, much effort was put into making exploration rewarding and interesting; many optional areas can be missed or avoided.
All retail copies of the game, as well as all initial digital versions, were bundled with Counter-Strike: Source, which some game journalists referred to as part of Half-Life 2's "multiplayer component." Half-Life 2 received critical acclaim, with praise directed towards its advanced physics, animation, sound, AI, graphics, and narrative, and is widely considered to be one of the greatest games of all time.
The game won 39 "Game of the Year" awards and the title of "Game of the Decade" at the 2012 Spike Video Game Awards, in addition to sales of 12 million copies by 2011.
Taking place some years after the events of Half-Life, protagonist Gordon Freeman is awakened by the enigmatic G-Man to find the world has been taken over by the alien Combine.
Joined by allies including resistance fighter Alyx Vance, Gordon searches for a way to free humanity using a variety of weapons, including the object-manipulating Gravity Gun.
During development, a substantial part of the project was leaked and distributed on the Internet.
The game was developed alongside Valve's Steam software and the Source engine.
The sequel has similar mechanics to Half-Life, including health-and-weapon systems and periodic physics puzzles, except with the newer Source engine and improved graphics.
The player also starts without items, slowly building up their arsenal over the course of the game.
Others use predictable but powerful attacks, while others hide before swiftly attacking the player.