Well, my opinion has always been Atom is a full x86 CPU. It will run all applications or games that can run on a normal desktop computer. It has a lot less performance in order to achieve a very power efficient design. But still, a modern day Atom is really in the same league of typical CPUs being used 7-8 years ago. So in term of raw processing power, that's still pretty impressive. Meanwhile ARM CPU is more like 10 years behind current desktop processing power.
As it is, current generation of Windows 8 tablet is able to play several older Windows games smoothly. Older classics such as Diablo 2, the earlier Sims, the earlier Heroes of Might and Magic, Galactic Civilizations etc should have no issue at all. The biggest issue would be the user interaction as touch UI is not that optimal for games that geared towards keyboard and mouse input. For that, there are several alternatives and workaround.
(1) You can run the game in windowed mode, and dock the onscreen keyboard beneath the window as input, with resolution as high as 1920x1080, there are plenty of screen space to accomodate that as older game tends to cater of lower resolution anyway. So you can have a 800x600 window on top, and still has 400+ pixels at the bottom for onscreen keyboard.
(2) You can get a bluetooth mini keyboard such as http://www.engadget.com/2010/03/05/rii-mini-wireless-keyboard-is-perfect-for-your-htpc-not-your-wi/, and use that for keyboard and mouse input.
(3) Finally, you can also use your iPhone/iPod/iPad or Android devices or Windows phone as input, by running an app which act like a keyboard and mouse for the Windows 8 tablet. Such as: