Kroos is class but I think he could do with imposing himself a bit more on games. Some times he seems happy to go through the motions instead of inserting himself when needed to. Not sure if that's because he already plays with some players with top class mentalities in the midfield but he might come into his own at Man Utd if the focus is on him.
Man U need someone dominant like, he'll be no use if he likes to Kroos through games.