herrera's attributes:
as a spanish he is a natural good passer;
he possesses good fundamental ball sense;
he is tall, which should allow him to cover up big area in midfield with relative ease;
his weaknesses:
his balance is not ideal, this is especially obvious when he makes twist;
he is relatively physically weak, he might want to gain some more weight to play in the premier league;
and the last is, his attitude and mind towards a game
from numerous interviews herrera has stressed on how much he wants to play in the no 10 role. however, despite he is a good passer but he still don't have the precision to make acute and agile passes in a small area within extreme fast speed. this is a very critical quality that a prolific no 10 needs to possess. in addition of his body balance is in question, i doubt he can excel in a no 10 role for us. he might be able to play there for a mid table club, but for a elite club whose always wants to build up an invincible squad, i'm afraid herrera will not be an ideal candidate.
in pre-season herrera was quite settled in a pure midfield role. but after the season kicked, he tried quite hard to prove himself is a no 10. we observed he had moved himself too up front and had exposed our midfield for opponents to counter. so, right now how he thinks he would be a player for united is quite essential in his play and his future here.
herrera has his quality. but i don't think he will become a pillar like keano. the best i can rate him is to put him into the same class as flecther, carrick alike. if he settles with a pure midfielder role, i see him as a quality addition to our squad. otherwise, he might let himself even to be a liability. nani is a good example how a quality player depletes.
he has just joined us for less than half a year. as lvg once said, there was competition inside our dressing room to build up a new hierarchy. i won't blame him for his ambition. but the earlier he can realize where his future lies, the better for him to settle in united.
i won't be too pessimistic about his future.