Complex DirectX 9 shader calculations allow for a very high level of realism as well as breathtaking effects, but these effects demand a high level of performance from the graphics card in a system. Owners of TFT screens are faced with the additional problem of having to play at a certain screen resolution if they want the best visual quality, since flat-screen displays have a fixed native resolution for optimal quality. All of this means that some of the older graphics cards, as well as the entry-level cards, may not be up to the task.
One problem for those looking to upgrade is that most newer cards use the PCI Express interface, and not every user is willing to upgrade their entire system to use PCIe. If the motherboard, CPU and memory still have some mileage left in them, buying an AGP card is certainly still a viable option, rather than buying new versions of all of these components.