Classics:
Freespace and Freespace 2 (Space sim similar to X-Wing or Wing Commander)
Half-Life 2
Left 4 Dead and Left 4 Dead 2
Newer or Newerish games:
Batman Arkham series
Middle Earth Shadow of Mordor, and Middle Earth Shadow of War
Tomb Raider reboot series
I also love flight simulators, so I'm looking forward to the new Microsoft Flight Simulator coming later this year.