Legion Hardware has the best and most comprehensive review so far
http://www.legionhardware.com/articles_pages/metro_2033_performance_guide,1.html
It shows that despite the physics being shared by the CPU and GPU, the game seems to be considerably more GPU intensive. Moving from dual to quad core makes no difference, and even a hefty overclock from say 2ghz to 4ghz also provides no noticeable difference.
The main killers of performance are rated in this order :
1. Anything DX11, so DOF, Tesselation etc.
2. MSAA 4X
3. Very High Settings
It's been my personal observance, that the game is 'playable' with a GTX 295, 4870x2, 5790(not mine), and Crossfire 5870(not mine), at :
1920X1200
DX10
Very High
AAA
However, whether because of poor coding or driver issues, the game loses frames unnecessarily in areas with certain particle displacement or advanced lighting.
(Using settings above)For interior sections of the game, the average I have mustered, is 50-XXX. However as soon as I run into an area that is heavily lit(artificial lights) or has floating particles, frame rates can be cut by more than half. Fortunately it's still manageable at 30 frames, and those areas don't last for too long.
(Using settings above)For outdoor sections of the game, the average seem to be more like 30-XXX. And what irks me about that, is the 'surface' portion of the game, has some pretty cheesy and awful looking visuals. Textures seem low, geometry isn't very advanced etc.
Additionally if you use MSAA4x, you get a blur over the entire screen. It's seemingly adjusting the negative LOD bias for textures. Or rather it might be that with MSAA off, the game uses the extra performance and forces a -1 negative LOD bias, which is why the textures look too grainy and saturated with contrast. I like a high contrast factor, but really, too much bias and textures will shimmer/crawl - it can also hurt performance.
I rather like how it looks with the bias toned down some because of the MSAA but it's just so painful to run. Alternatively, DOF would reduce some of the LOD bias(to your eyes at least), but it also crushes the performance.
All in all, I'm not impressed with the visuals, but I do like some of the scenes they've created, and the sense of immersion you get. What disappoints me, is that a good portion of the areas are very 'playable' in terms of performance, but then just when you think you're going smooth, you get slapped in the face because there's a few dust particles floating around.
Where as(previously mentioned before), I look at something like Risen, and realize that a game where you can use shadows with a texture map up to 4096 or even 8192, and has a very similar set of art that was popular in the Crysis games, is bound to be demanding on a system, and it is, but it's demanding pretty much all through-out.
So it's the inconsistency of Metro that's upsetting.
Gameplay as said before is good, a bit more engaging than most, though it's kinda like Predator in AVP. It's cool at first; different ways to kill enemies, go in strong or go in quiet, but after a while you feel like you're on a set of tracks and you get bored.