Having just completed Half Life 2, and having enjoyed it considerably (despite having to wait over 8 hours for my single-player files to unlock on my dial-up connection) , it made me think that I really enjoyed System Shock 2, and felt a fair bit more terror and achievement over the course of its narrative than any other FPS.
Will there be a fair quantity of nervously-cleared throats and callously-trimmed jibs over this pontification? I imagine that this sort of thread gets introduced frequently, but let's try to keep the Multiplayer *twitch lan session* kiddies out of it for a minute... the title for the best *non multiplayer* FPS up for grabs here.
For me, the story, the fear, the gamepig... system shock 2 surged to the head of the pack in terms of awesome single player FPS experiences, followed closely by No One Lives Forever, Undying, and Half Life.
Did you find SIN a miracle-work of genious story-telling? Did Mortyr bring tears to your eyes for its depth? I've missed many a single-player FPS over the years, so let us hear the ones that made the biggest impact with you!