the sequel of L4D, we totally recommend this one

a funny zombie game, the sickness of the city is quite interesting, The Green Flu

a Online version of HL2

also a great game.

its a game much like Left 4 Dead 2, but then with a storymode

a game where you can pull some pranks on, like MVM tanks with Half Life medic

The same as TF2, we never tried that, but it seems to be fun