I ran the game at 1024x768/16 Bit/High Details on a c533A@825/128MB SDRAM/GF2 64MB and got BAD chop whenever there were particle effects or massive outdoor areas/textures. The framerate was somewhere around 25 FPS This was using the D3D Beta patch, which did NOTHING to improve the framerate. I found this performance tolerable, but it's still inexcusable for a year 2000 game to not produce +50 FPS with that kind of system at those resolutions/color depths. I get ~90-100 FPS in Q3A at 1024/768/32 Bit/High Details and around 50-60 FPS in UT using D3D at same graphic settings.
As I understand it, DX uses a newer build of the ORIGINAL Unreal engine, not the UT engine (whatever that means). I tried using various UT D3D DLL builds in DX and they wouldn't work.
As for the game, its good, not great. First of all be warned , this is a LONG game. It took me about a month to finish playing about 6-10 hours a week.
I really hated the NPC interaction, finding it tended to slow the action considerably and really rip me out of the character since critical discussions are done in 3rd person rather than keeping the first person perspective at all times.
The "open design" is really not that open. There's basically 3 methods for accomplishing any objective: Brute Force, Stealth, and Information Gathering, and of course combinations of those three methods. The way they allow this is by creating redundant "paths" through the levels. This again was more annoying for me than involving. For example, say you need to get into a locked room (innovative huh?). Many times you end up finding within a 50 foot radius of that room a data cube conveniently laying around with a secret code to hack a security computer, a floor grating you can crawl through to reach that room, or a stash of ammo/heavy weaponry/TNT crates with which to blow open the door. The levels though remain basically linear. The decisions you make only really effect the fate of some minor characters and whether some side quests become available to you or not. This is kind of a spoiler, but the different endings are not necessarily inextricably linked to certain decisions you made earlier.
Anyway, being a big fan of System Shock 2 I was hoping for more than I got. Like I said, good game, but not great in my opinion.
). My friends 32MB GTS' seem to chug too at times. 
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