Natural Selection is a classic man. I used to love playing The Hidden mod too along with the plethora of Garrysmod gamemodes. I really do miss the source mod hayday.
@smokerob79 How is that New California mod? I'm always worried about the quality of writing and voice acting when it comes to fan made projects of that scale.
HL2, Max Payne 3, Portal, Wolfenstein, Bioshock, Black Mesa, Control, L4D, Doom
I just really enjoy playing one or two missions from old(er) games occasionally, That increases with new hardware.