I've always been a fan of F.E.A.R.
It was an exceptionally well made FPS game that took a break from all the WW2 and scifi shooters that were popular in the mid-2000s.
*The combat was high-paced, with exceptionally intetelligent A.I.
*The enviroments were claustrophobic, which added to the gameplay and horror.
*The story was interesting - Militaristic SciFi & Ghost Horror.
And how these three factors were interwoven within the game made it one of the most original games of the last 20 years.
I need to get around to playing it again. Its been about 8 years since I last played it, and my laptop could easily play it at full resolution, graphical details, at 60+ FPS. And I'm much more tactical in the way I play shooters, after playing CounterStrike for 600+ hours.
It'd be interesting if it could be remade/rebooted for modern rigs/consoles.