I don't think there's any question as to his coaching ability. He has a proven track record of success.
Other than that, I don't think he's well-respected amongst his peers. He has a long history of diva behavior and rubbing people the wrong way, and, his recruiting antics are creepy and self-serving (there is no excuse for sleeping in a recruits bedroom - ever).
I don't recall which QB it was that was in his draft class (it may have been Kelly Stauffer), that ended up as an analyst for either ESPN or the NFL network, but, he gave a scathing review of Jim Harbaugh about seven years ago or so. It was fascinating, as you rarely see one player call out other players for their personality. He relayed a story about when all of the draft's QBs were attending some type of pre-draft camp, and, when waiting for the bus, Harbaugh stood by himself and didn't interact with the other players. After a long wait, he became frustrated and announced that somebody like him shouldn't have to wait, so, he hailed a taxi and went by himself.
Then, there's other well-documented incidents, such as breaking his hand punching Jim Kelly, the back-slapping incident with Jim Schwartz, and, ragging on Michigan's academic standards and coaches before accepting the contract offer. Lloyd Carr, a good guy IMO, had nothing but scathing things to say about him.
You're more than welcome to like him, but, I'll pass.