I don't know what kind of a manager he could turn out to be in a long run but I think he has done well so far.
Strangely I have a little crush for Eintracht Frankfurt so I watch a little bit of their games. To realize how well he did there you need to understand that before him they were really dire. He did a stirling job there. Apart from the obvious achievements (imagine the Watford or Norwich teams of this year easily finish in the mid table next two seasons and making wild cup runs) he improved his players immensely. This saw the club making very good profits of some of their players.
As for the Bayern players criticizing him. Well, they could be very arrogant bunch at times. I remember them doing the same with Trappatoni and Ancelotti more recently. Obviously, they haven't done much better without Kovac either. However, it is true that throughout his tenure at Bayern there was a constant feeling that this job was too big for him.
