Indeed, Mufasa was so wise, brave, powerful and majestic. Someone that mighty being so great in spirit. Simba has SOME of Mufasa's qualities, but he sorely lacked the wisdom and patience of his mightier father.
I have a pretty good idea what he is upset with Simba.
Mufasa: Simba what have you done!?
Mufasa: You banished Kovu without letting him explain what happened! And to confine your daughter in priderock like a prisoner because of what happened!?
Simba: But father! Kovu was using Kiara to get to me!
Mufasa: At first yes! Simba, he was raised by a hateful lioness to be a weapon, he didn't have any choices or escape, Kiara saved him and he wanted to tell you Zira's plot! And he had nothing to do with the ambush!
Simba: Zira made it clear that Kovu was Scar's heir, I know he is following his pawprints, and if I haven't escape he would have taken over priderock and Kiara would end up dead.
Mufasa: No she wouldn't! And how could you be so cold to her!? She knows Kovu better than anyone else and she knows that he loves her! She is an adult now Simba, she can make her own choices and decide for herself and she is smart enough to be a judge of character. You have no right to trap her here and treat her like a child!
Simba: She is young and doesn;t know what she wants! And whether she likes it or not, Kovu will not come back.
Mufasa: (glares) What's happened to you? You have become more cold and bitter over the years, Kiara is right, you can never be me and she is more of an adult than you are because she is willing to give people a chance while you isolate them and are cruel to almost every being that comes here..you are not being me...you are becoming like Scar.
Mufasa: If you don't change your ways and let go of your hatred Simba, not only will you turn everyone against you, you will lose Nala and Kiara, and end up like your uncle..I hope that you are prepared to face the consequences if that's the case.