Half-Life 2 is a first-person shooter video game and the sequel to Half-Life. Developed by Valve Corporation, it was released on November 16, 2004, following a protracted five-year $40 million development, during which a substantial part of the project was leaked and distributed on the Internet.
The game was developed alongside Valve's Steam software. It introduced the Source game engine and, because of Steam, was the first single-player video game to require online product activation.
Like its predecessor, Half-Life 2 is a single-player first-person shooter broken into several chapters, permanently casting the player as the protagonist Gordon Freeman. The sequel has nearly the same mechanics as Half-Life, including health-and-weapon systems and periodic physics puzzles, except with the newer Source Engine and improved graphics.