He's a great manager, despite his downs (he really seems to run a team into the ground after 3 seasons), and I would put him up there among the best. The main issue is he's not very consistent. He pretty much always gets a few trophies in the first and second year, but then in the third everything just goes bad and he gets fired.
Despite all his triumphs, he just comes off as such a douchebag. Comparing him to Klopp (which seems fair after today's game), it's day and night. With Klopp you have a guy who is smiling and laughing during the interview, he's very passionate about football, his team and the people around him, and he's also very humble. Mourinho on the other hand is the same dead, cold self that he has always been. He's sarcastically applauding decisions by the referee that go against Chelsea, he confront referees in the player tunnel and gets sent up, he never takes any responsibility or gives the other team any props for their victory. Some words you will never hear from Mourinho's mouth are "The other team played better than us today and they deserved the win". Sure, a lot of managers are bad losers, but that combined with everything else he's doing.. blaming FIFA, UEFA, the medical team, the guy responsible for the water bottles, the weather, and he also takes the time to applaud players like Costa and encourage shitty behavior on the football pitch. When he as a manager pokes the eye of the assistant manager of the other team (Real vs Barcelona a few years back), he sends some really weird messages to his players about what is okay or not.
I still think he is an excellent manager, but he goes out of his way to be as big of a douchebag as possible. He might be the nicest guy ever, and spend time with his kids, wife, be kind to his friends, but he has built his whole image on people hating him and that it's always him against the world. Everything I've already said, plus the fact that he always plays very defensive football with the main object of scoring a goal, then tackling, defending, using every dirty trick to injure other players, make the time pass faster and get the result.. it doesn't make him very sympathetic.