The only game I have that uses GFWL is Dawn of War 2 and it's broken. It shits it's pants auto updating and I can't be fucked fixing it. When it was "working" everything about it was opaque and you still had to run steam(A superior program) in the background, but it handled everything steam did, but worse. Voices are mangled/distorted, lags, bad match making, loses connection to server more often than Bnet(Better, no where near steam good). GFWL is obviously windows only, which is a backwards thing these days and even if they offered it for Mac, I wouldn't take it. Stacks on top of any other client/drm without offering anything good in return.
MS can take it's gaming Future and
SHOVEL it.
That said, Mac App Store isn't any better. Overpriced and does nothing for the customer. You might as well just buy direct from the developer if you can. I would stay away from it like it's the plague.