for me this.

2560x1566

Plants vs. Zombies
Crysis
Dead Space 1+2
Starcraft II
Diablo III
Grand Theft Auto

Depends on me : I think the best PC Games
RPG : The Elder Scrolls Series , Torchlight 2
FPS : Battlefield 3
Horrors : Amnesia

the others : Dishonored , The Walking Dead , Sleeping Dogs

Well, considering the old times, the game that have been being (widely) played since it first came out is counter-strike. For myself, i still play cs 1.6 online using garena:) thats why im gonna vote for

Counter-Strike.

Besides that, im a blizzard fan, so i'll go with StarCraft II.

Battlefield Series
NFS U2 / Carbon

SKYRIM! with mods (if you know what I mean) ;)

gta 4
limbo

Definitely: Guild Wars 2
Borderlands 2
Mass Effect 3

Team Fortress 2
Trackmania
Dota 2
Half Life 2
Crysis
Medal of Honor