3. Left 4 Dead
I've never been much of a co-op gamer, gaming has always been a solitary and pious endeavour for me... until this came along. Although L4D didn't exactly reinvent the co-op wheel - and there was a bit of a nerd furore when a sequel was announced as opposed to expansions - this is here due to the amount of fun you can have. The kitsch presentation of its campaigns as zombie flicks - complete with credits and ace B-movie posters - is a nice touch, but the true beauty of this game is how it imbues bickering paranoia and selfish survivalism among its players, making us subtly recreate the tone that has been a staple of zombie films since the genre was born-proper with Night of the Living Dead.