Is everyone in here running the game with EAX enabled? I ask because that was the huge framerate killer for me with the game. For example, the beginning of the map (outside) where the world is covered by that organism...EAX enabled - roughly 12-22fps, EAX disabled - roughly 50-80. I'm on an XP1900+ and 9700Pro and am running 1280x960x32 with 4xAA and 8x performance aniso, all display options are set to maximum in game except shadows which I have set to medium. I may have been running only 2xAA during the number posted above but can't remember for sure, 4xAA seems to have nearly no performance hit over 2xAA though as I seem to be almost entirely CPU limited in this game with only a 1900+.
I agree the game could run better, but I'm fairly satisfied considering the visual details I'm running and the fact my cpu is over a year old. I wouldn't be happy with the framerate I'm getting if this was a faster paced and/or multiplayer game, but with the pace the game moves I'm fairly happy with ~40-80fps. I do get dips down to around 30fps on occasion though in certain spots.