A lot of people have been wondering what he offers.
I think this performance highlights that well:
He's not your technically absolute immaculate like an Isco, Silva or Iniesta, but he's a proper match winning attacking midfielder/forward. One who is good with the ball at feet, is a good passer, has enough pace and physicality for a central role, and a gem of a left foot. Mata with pace and skill to beat a defender, and physical presence, if you will.
If we're going to play at a high tempo with quick transitions next season, then this guy is the ideal #10, and a huge improvement over Mata and Rooney. If we're going to play slow possession football, he will struggle.
All subject to his attitude being right of course.