I regularly replay older FPSes (probably more than I play new ones actually), so I’d be interested to hear from others who do the same. PC platform, 2006 or older. You regularly replay it, you ...

Undying was great. It doesn't maintain the creepy level throughout, but it's still pretty good. Might have been the first game where you have use both hands. I have fond memories of Rise of the Triad, ...