The demo was was way late on this game, like way after it came out.
If you have the hardware to play it on very high, check out the textures,particles (smoke/ fog) and the advanced DOF. It's really quit something.
I believe I read that the Demo runs the first 4-5 scenes and is fully equipped.
Watch for it on steam, you can get it for $20.00 about every other week. I think Walmart has it @ 19.99 always.
Not to be a stick in the mud, but it will bring your VGA to its knees. This is some benchmarking I did with my quadfire rig using 2x 5850's, 3 x 5850's and 4x 5850's
Its a killer .
https://www.techspot.com/gallery/data/500/medium/metro_2033_bench_3.JPG
https://www.techspot.com/gallery/data/500/medium/metro_2033_bench.JPG
This is all settings maxed out @ 1920 X 1080, if you tweak it though, you can get it playable with less and it will still look very good.
happy gaming