I downloaded the demo and played through it today.  It runs very well and smooth with all the effects turned up.  It seems to be a decent game single player wise but I didnt notice a whole lot that made it stand out above the other FPS's out there.  The gravity walkways are kinda cool but it wears off pretty quicky even in the demo.  Graphics are nice and even look better then quake4/doom3.  I'd give it a C+...  But thats my opinion on a demo of the full version and Im very partial to multiplayer games.  Let me know what you guys think?