Small side games released around the time of the original include the multiplayer game Half-Life 2: Deathmatch and the single bonus chapter Half-Life 2: Lost Coast.

Breen, former administrator of Black Mesa and now self-styled overlord of humanity. In this, he is aided by the Vortigaunts, an alien race whose enslavement he broke by his destruction of the Nihilanth members of the Resistance, including several former Black Mesa scientists and Action Girl Alyx Vance, who accompanies Freeman throughout much of the game as a fully-qualified AI partner. Having attained an almost messianic status among the fledgling resistance forces thanks to his actions in Black Mesa, Gordon attempts to survive and eventually strike back against the Combine by provoking a full-scale revolution. Gordon soon finds out that Earth has been invaded and conquered by a powerful alien force known as the Combine, which apparently detected the Black Mesa incident and took advantage of it to enslave humanity and add Earth to its collection of assimilated worlds. Half-Life 2 starts off about twenty years after the ending of the original game, as the mysterious G-Man uses his time- and space-bending powers to place Gordon Freeman on a train headed for City 17, some undisclosed place in Eastern Europe. Every retail copy of the game also came with Counter-Strike: Source to help fill out the multiplayer side of things.

In 2004, Valve released the sequel to their revolutionary and critically acclaimed first game Half-Life 1, Half-Life 2, which itself broke new ground on many fronts in its graphics engine, physics system, artificial intelligence, and its online distribution/updating system.

Half life 2 episode tree