The game was developed alongside Valve's Steam software. It introduced the Source game engine and, because of Steam, is the first video game to require online product activation.
Like its predecessor, Half-Life 2 was met with near-unanimous critical acclaim. It was praised for its advanced physics, animation, sound, AI, graphics, and narrative. The game won 39 "Game of the Year" awards, and a couple of publications have named it "Game of the Decade". Over 6.5 million copies of Half-Life 2 were sold at retail by December 3, 2008, making it a bestselling PC game (not including the number of sales via Steam). As of February 9, 2011, Half-Life 2 has sold over 12 million copies.
Read more about Half-Life 2: Gameplay, Development, Critical Reception