HL1 > Quake 1 > BF1942 > Medal of Honor > Heretic 1 Serpent Riders> Halo 1
Notice all teh 1's?
BTW Although Quake 2 was fun, I really got bored near the end. Quake 3? I really prefer the story/SP experience.
To me Halflife had the finest sound effects, scare factor, and gripped me in front of the monitor longer than any other FPS.
Quake 1 put me in a mood. As usual id is the masters of environment and mood, and Quake 1 really helped me immerse my depressive life into this bloddy 256 brown/green morbid Trent Resnor world I loved to bathe in.
BF1942... Simply the funnest start up an go MP FPS i've ever played.
MOH: Because its just really good fun, and I like WWII shit.
Heretic1 Serpent riders, for its environment and weapons. Plus those magical and demonic characters and chanting wizards really creeped me out
Halo 1 because it was hard but so beautiful and rewarding to me. Long game too.