HL2 really hit me the hardest. I felt like it was a real experience. I've always been fascinated with underground resistance, oppression, civil collapse, fleeing enemies, etc so HL2 was like an actualization of some of my favorite scenarios.
FEAR was good because of the paranormal aspect as well as the character twists.
I'm playing Crysis right now but High Shaders takes a huge toll but looks too amazing to turn down.
I bought gears and crysis at the same time. I FINISHED gears, crysis i have only made it to the 2nd stage. Gears is just a much more fun game in my opinion.