Re: Wow, this game is a system hog.
I'm running on a Geforce FX 5900 Ultra with a 3.2 ghz processor, 1024 MB RAM, and framerate is fairly constant, around 30-45. All settings set to High (AA 2X, AF 4X), with the exception of Shader quality (Default value is high quality; lowered it due to personal preference).
Still, SinE does run worse than HL2, although I'm suspecting this is more related to mapping (use of area portals, HINTs, etc.) rather than actual 'code'.
Edit: I'd suggest you get more HD space; it does wonders to in-game performance.