I don't know if they're the worst, but how good has MS Studios actually been? They've acquired developers that had already made good games, like Bungie, Lionhead, Rare, and Twisted Pixel. They shut down Ensemble completely. And how good have games been under their care? Halo 2's production was a mess. Halo 4... well. Forza has generally been good, but the latest one is catching flak for a bunch of microtransactions. Rare has made, what, KI and Kinect games? Fable has been pretty good. My perception is probably skewed, but it seems like MS hasn't managed their first-party IP's that well. We're still waiting for Black Tusk though.