It is really difficult to pick one but if I have to, I guess F.E.A.R. the first installment. The 2nd and 3rd was kinda botched. Story was rushed, graphics changed too much not the same. Dont get me wrong Fear 2 Project Origin and F.3.A.R. the 3rd one is fun to play but its not on the same level as the 1st one. That one was really fun. Is really fun I still play it sometimes. I heard the NPCs, the monsters and soldiers you have to blast actually had quite a good programming in their ai. Compared to a lot of games it stand out well and it was made by one guy I read from an atricle some time ago.
https://www.rockpapershotgun.com/why-fears-ai-is-still-the-best-in-first-person-...