I think people are going overboard with some of his performances. His best game was undoubtedly against LA Galaxy, who were by far the worst opposition we have faced, but none of his performances following that match have come remotely close to that sublime performance. He's clearly a quality player and someone who adds to our midfield and will improve, but he's not without his faults. Definitely our best midfielder, but I suspect there is certainly a lot more to come.
Just to elaborate on a few of his weaker sides to his game, I wouldn't include tackling or his combative nature in that side of things. He is what he is and our midfield has been so passive and tentative for years, it's vital we possess a player like Herrera and he is always going to be prone to a few poor challenges. What slightly concerns me, is not so much his passing itself, but his use of the ball in certain areas of the pitch. His passing is generally impressive. However, I've noticed how frequently he gives away possession in our own half - not just last night, but throughout the tour - and this is when 5v4's in favour of the opposition can occur, when he's often the deepest midfielder.
The signs aren't ominous that he will continue to make those mistakes, but it could prove decisive against very good pressing sides. Another thing is his tendency to overcook passes. He has excellent vision and can execute very impressive through-balls, but his consistency in doing so fluctuates a bit too much and the direction and weight is often off when attempting what should be considered a relatively simple - compared to others - pass. If he can find a better balance between his passes in our third and the oppositions, he will be far more lethal and potentially less liable.
That's just a few criticisms, but I'm very excited to see how he develops here. On a more positive note, some of his touches are exquisite and his awareness of teammates around him is incredible. A very well-rounded player.