Originally I was thinking of having a poll just restricted to Far Cry and its descendents, but, hey, Cryostasis and DM(m)C can join the crying party too :'D
I absolutely love Cryostasis - extremely creative and a fantastic atmosphere. Shame about the poor optimisation.
Crysis was really something special to me - even when I played it for the first time years after its release - I especially loved that middle level.
DmC Devil May Cry - I had never played a Devil May Cry game before, so I didn't have much in the way of expectations, but I really had a blast playing it. There's also some areas with stunning visual design.
But my favourite would have to be Far Cry 2 - I found it to be incredibly immersive. I just loved being within the game world, even if it meant having malaria. To me, it was such a wonderful experience.
Blood Dragon. I jump-laser-stabbed so many dudes. And then the end auto-scrolling bit was fantastic. That entire game was 110% in the "stupid awesome" category.
The Battle Armored Dragon Assault Strike System. Because of fucking course it would acronym to BADASS. "Your Killstar controls my braincage, instructing me that you are my rider." "And I shoot lasers out of my fucking eyes." (and then he shoots lasers out of his fucking eyes).