You wouldn't necessarily be comparing CPUs here, though that will be part of it. GPUs are what run most graphical games which I assume the OP is referring to. Plenty of 3D FPS and RPG available on ARM devices.
Yes, some smartphone GPUs are more powerful then older Intel HD graphics onboard a CPU. And some tablets have a lot more thermal headroom then smartphones and can be quite powerful. IE the Nvidia Tegra series chips. The Tegra 3 has 1/4 of a full Fermi desktop graphics card, and that is nothing to sneeze at. The Tegra K1 has a 1/4 of a Kepler GPU. The new X1 has half of a low end Maxwell GPU.
And the Adreno GPU series and others aren't far behind.
You would have to list the exact specifications of the computer in question to get a better answer.