Half-Life 2 was followed by a free extra level, Lost Coast (2005), and the episodic sequels Episode One (2006) and Episode Two (2007). Valve released a deathmatch mode in 2004. It won 39 Game of the Year awards, and has been cited as one of the best games of all time. Half-Life 2 was released on Novemand received acclaim for its advanced physics, animation, sound, AI, graphics, and narrative. A year before release, a hacker stole an unfinished version and leaked it online.

Valve announced Half-Life 2 at E3 2003 and released it through its new distribution service Steam after delaying it by over a year. Valve president Gabe Newell set his team the goal of redefining the FPS genre, focusing on advanced physics systems and non-player characters. Development lasted five years and cost US$40 million. The game was created using Valve's Source engine, which was developed at the same time.

Set roughly twenty years after the events of the first game, players control Gordon Freeman as he joins a resistance movement to liberate the Earth from the control of an alien empire called the Combine. Like the original Half-Life (1998), it combines shooting, puzzles, and storytelling, and adds features such as vehicles and physics-based gameplay. Half-Life 2 is a 2004 first-person shooter game developed and published by Valve.