He was very solid for Spain during the U21 EC last summer. I did not read to much into it at the time, because its very difficult to judge a player based on a performance in a tournament like this. Actually I have not seen much of him since, but on Thursday I was very, very impressed.
He put down one of the best midfield displays I have seen at Old Trafford for a very long time. According to Telegraph he had 96 passes, with a completion rate of 91 %. That is more than Giggs and Jones put together. Iturraspe and Martinez was second on the list with 63 passes (and a completion rate of 90 for both of them). He was obviously the focal point of their team, and a player who always was available for a pass. That is a great quality to have. He also had an excellent work rate, and came across as a player who could play in a 442.
With great technique, awareness, quick feet (though not fast) and intensity to his game he came across as a typical, well schooled, Spanish midfielder. That is obviously a compliment these days, and just as obvious a player we lack in our team. Herrera proved that he is definitely one to watch for Ferguson.