I keep trying to spot patterns with the people who have problems having Ati/nVidia cards or AMD/Intel processors and so on and so forth, but there seems to be no rhyme or reason to all the performance problems. There's something very subjectively weird going on if someone with an XP3000, a gig of RAM and a 5900 can't run it, and someone with a XP 2100, half a gig and a 9500 can run it like silk.
I think PART of the problem is people's expectations. On my machine, it's no "slide show", but it's not "smooth as silk either".
I'd have to guess around 30-40 FPS at 1024x768 (without ini tweaking). This is fine for me, as I liked playing DX at a slow pace (sneaking around was fun). But considering it doesn't have ground-breaking graphics, I'm slightly dissappointed. Then again, the original DX was a hog on mid-range PC's back in its day.
However, my problems with the game aren't so much performance, but with style and interface. Try hacking a security terminal, and tell me it's not dummied down. It went from elegant mouse interface with nice screens to 1996 option menu.
My stats:
Intel P4 2.4GHZ w/ 533MHZ FSB
1GB DDR 2700
ATI Radeon 9800 XT w/ 256MB (catalyst 3.9)
SB Live! Value Soundcard
WD 80GB HD w/ 7200RPM and 8MB cache
Windows XP Pro
"Space. It seems to go on and on forever. But then you get to the end and a gorilla starts throwing barrels at you."
-Fry, Futurama