Sunderland beat Man City and Everton too, and Everton had only lost once before that match. They were awful under Di Canio and his awful rules and freezing out their better players, but they look solid under Gus. It's not like Swansea and Tottenham are bad clubs either, which Man Utd also just lost too. However, I'm pretty certain they would've grinded out much better results under Ferguson. After several years of watching that magician making title-winning teams out of a bunch of average players and a few world class players, it's kind of nice to finally see them falter.
Kagawa is very light-weight and Rooney is better than him in the deep lying forward/advanced playmaker role, which is Kagawa's best position. Kagawa is pretty bad on the wings, and doesn't really warrant starting just now. Nani can be anything from great to awful. He wasn't one of the first names on the team sheet in Ferguson's last season either, probably because he can be a liability.
I believe Man Utd can improve a lot by signing a class central midfielder, something they really lack (what does the likes of Cleverley even do?) but are they attractive enough to bait the very best just now? I'm not so sure.