RAM: 8GB minimum
GPU: GTX590 or HD6990 or greater
GPu index chart: http://www.tomshardware.com/charts/2011-gaming-graphics-charts/Metro-2033-Gamer,2663.html
From there everything else optional, i would recommend a drive no larger than 1TB for games realistically a 250-500gb for gaming and a 1TB+ for archive storage... big platters = poor performance..
I suggest grabbing an AMD Bulldozer for the CPU they are cheap and living monsters for crunching numbers, your GPU can offset any gaming bottlenecks.
as a bonus this rig could run a VM while running Crysis 3 at the same time ^_^