Picked the game last night - reasonably fun so far. The enemy AI is good, so it is not just a mindless shooter, and can be challenging at times.
I have to say though, even with all gfx settings on high, specular lighting on, etc, the game looks pretty dated. Character models and terrain are blocky (less noticable inside), vegetation looks like crap. Sky box is awful and pixelated - which is too bad because the imagery is cool. The game is really showing its age. The main bummer is, to get a good framerate, I need to drop to 800x600, turn off anti-aliasing and turn off specular lighting. When you do that, the game goes from looking dated to looking like total crap.
Music and atmosphere is great, the voice acting is horrible.