I'll only list PC games since console games from when I was little won't count (hard to play those today.)
Elder Scrolls 5: Skyrim
Fallout: New Vegas
Fallout 4
Vampire: Masquerade
Vampire: Bloodlines
GTA5
GTA: San Andreas
Witcher 3
Far Cry 3
Insurgency
State of Decay
Gothic 1 & 2, but not 3 and 4
Deus Ex 1 & 2
Left 4 Dead series
Star Wars: Knights of the Old Republic 1 & 2
Games people here should play, but haven't mentioned in above posts (they aren't popular:)
Gothic 1 & 2
Vampire: Bloodlines
Both of these are solid RPGs that are both extremely underrated. They both are older and make take some playing around with your PC to get running, but once you do...
Gothic 1 and 2 are like what you'd get with Witcher if it was made like 15-20 years ago basically. Just understand these games are old and somewhat glitchy on modern machines.
If you're curious on Gothic lore this is a great introduction to the series:
If you get Vampire: Bloodlines get the unnofficial patch mod to make it work.