9. The Source Engine
It may have made its debut with 2004's Counter Strike: Source, but Half Life 2 was the first game to truly show us what Valve's superb engine was capable of. At the time of its release, Half Life 2 blew gamers away with its groundbreaking graphics, which were also supported by the immensely realistic physics of the source engine. It certainly wasnt the first game to introduce realistic physics - the much ridiculed Jurassic Park Trespasser
had experimented with physics puzzles back in 1998 - but it was the source engine (with implemented Havok physics) which successfully implemented realistic physics into a game world. As well as the much touted use of realistic physics in Half Life 2, the source engine allows for incredibly detailed facial expression on characters, responsible for making Alyx Vance such a believable character. Since Half Life 2, Valve has taken the Source engine to new heights with such games as Left 4 Dead and most notably the Portal series, which expands on the physics puzzles of Half Life and forms an entire game of mind bending test chambers. Rumour has it that Valve is on the brink of unveiling an upgraded version of the engine for next gen consoles could this be the reason why Half Life 3 is taking so long ?