2. Half-Life 2
Back when Valve used to make their own games, their name almost became a byword for strong characterisation and unparalleled narrative. Certainly the original Half-Life was showered with praise for those very reasons, but it was this sequel that indelibly changed the shape of the video game landscape. The sense of place in Half-Life 2 is worth the price of admission alone, not to mention the superb AI, epic (yet intimate) yarn, and the fucking gravity gun - a weapon we've all been dying to again pull the trigger of for the last 5 years. Still, broken promises and absent sequels aside, you owe a whole lot to Half-Life, whether you want to or not. Now pipe down.