Take any screenshot of Half-Life 2 and chances are you'll be able to pick out a handful of influential things that have gone on to spawn countless titles - Valve's physics-sandbox masterpiece hit the ground sprinting, and has just as much to offer anyone today as back in 2004. Many games have those levels where everything just 'clicks', and in HL2 as soon as you were given the Gravity Gun you were waiting for a sequence that would play to its strengths i.e. something to let you get crazy with the in-world objects and hurl them at anything in the way. Luckily Valve had you covered, and at the exact moment you realised you could use the gun to slice a string of Head-Crabs off the top of many a zombified host in quick succession, this was immediately Greatest Game of All Time material.
