First, I wish Comey had waited a few more months to put this book out. I think Comey has had an successful unblemished career at the FBI. I think he has integrity. I will say that he displayed poor judgment with regards to exposing the status of Hillary Clintons case, which just should never have been discussed. This especially in the light of the Russian revelations that were coming out. Supposedly, there were no ties to Trump or his campaign at the time this was coming out, but not a word. And then doubling down, at the last minute that there may be more emails to investigate on Hillary. Although I agree with his description of Trump, I think the book is somewhat self serving, and may even complicate Mueller's investigation. I see nothing partisan about it. He is a Republican you know. Just not the flavor Trump likes.
EDIT: disclaimer, I have not read the book and going on preliminary reviews.