I like co-op PvE FPS and play them most of the time. These are some of my favorites:
- Left 4 Dead 2 (Realism Expert, Nesrealism, Hard Eight)
- PAYDAY 2 & 3 (now playing only 3)
- GTFO

Favorite single player games:
- Black Mesa
- Dying Light 1 (incl. The Following), Dying Light: The Beast
- Far Cry 3
- Half-Life series
- Metro series (2033 Redux, Last Light Redux, Exodus)
- Need for Speed: Most Wanted (2005)
- Portal series + mods (Reloaded, Stories: Mel)
- A Plague Tale series