Please note that the graphics cards inside the iMac are not desktop cards but laptop cards.
What's in the iMac is a HD 6970M, which I think is a underclocked HD 6850.
It can play all current games on high-ish settings, but it's not really a great graphics card for gaming on such a big monitor.
You can use the iMac as an external monitor for a gaming PC though in case you ever want to "upgrade".
I am not sure running games on a Mac is the same thing as a PC....even through Bootcamp....
Wait for a Mac gamer to answer (if there are any..lol)
All the best Brett
Bootcamp allows you to natively boot Windows on a Mac. Gaming works just as well as on any Windows PC with comparable hardware.