Runs great. I usually only play standard maps on it, not sure if it would bog down in end game on huge maps.
You need to figure out the scaling, and I prefer the mouse over the touchscreen method, but touchscreen does work for airplanes and stuff. I also like to hook it up to a large monitor, and then play away!
Oh, and the Surface is definitely worth the cost. It does everything the IPad does, but runs all Windows compatible software (including a bunch of games). There's posts in /r/surface about playing League of Legends, WoW, and some of the newer games on lower settings just fine.
As a laptop, its a completely comparable ultrabook. The battery life isn't Awesome, but decent.