The stated minimum requirements are enough for the game to play quite well. Many sub-minimum systems will also play the game if you compromise a bit.
Minimum CPU: Core 2 Duo, Athlon 64x2. Any x86-architecture CPU more modern than these is fine. I wouldn't expect competent performance from anything less. I know it doesn't run for crap on a Pentium D. We used to have a member who regularly complained that he couldn't run it on his Athlon XP.
Minimum RAM: 2GB. It really does run in 2GB. Some have gotten it to run with as little as 1GB. But I think it'd be plagued with delays.
Minimum Disk: This game has a big footprint. Have 30GB free on the volume you're installing to. If you're downloading, you'll need up to another 15GB for the download.
Minimum GPU: This is where the requirements get tricky.
The requirement for 512MB VRAM is important. GPUs with shared memory will perform poorly, and GPUs with less than 512MB will have rendering problems.
The minimum cards (AMD HD 3850, nVidia 8800 GT 512) are superior to many more recent cards. Most of the people who think they meet the requirements then get into trouble have a recent low-performance card. In my experience, the raster output processors (ROPs) on the card are the limiting resource.
The stated minimum cards have 16 ROPs. Any more recent card with 16 or more ROPs will play the game pretty well; ones with 24, 32, or more will reach high settings and high resolution.
Cards with 8 ROPs are below the minimum, but most will perform decently. Cards with 4 ROPs will frustrate most players. Intel integrated GPUs will barely play the game at all.
