A "full desktop OS" on hardware which lacks the horsepower, input mechanisms, and screen real estate required to compete with desktop gaming systems.

The very first version of the Surface Pro can run most Source engine games fairly well at the moment, and that's a situation which will improve rapidly if they keep iterating.

As to input mechanisms and screen real estate, it's still a Windows PC, that means it comes with all the advantages of one.

The important bit is that it's not a system any serious gamer would ver consider using, even if t could handle modern games.