What kind of Mac do you have?
The graphics will not be the same, as it uses a virtualized graphics card,
I don't mind it at all, however I choose to dual boot with Windows 7 (boot camp).
Parallels 4.0 requires additional RAM, Processors and graphics memory to run (on top of OSX).
Optionally, you can also buy Parallels 4.0 and get it to run from your Boot Camp partition, basically this means you can game on OSX with Parallels 4.0, or you can boot into Windows (boot camp).