I'm over halfway through. It's about 500 pages, and absolutely genuine. I doubt it was ghostwritten judging by the feel of the book. Bret is very open about ALL of his career, from drugs use to women, from family problems to happier times. He's not bashing anyone for the sake of bashing and I really think he put a lot of time and effort into this. He's even mentioned Shawn Michaels a handful of times and done nothing but shower the man's athletic ability with praise while refraining from comment on backstage behavior, because quite frankly the entire dressing room is behaving like idiots.
I've been blown away. If I had to rate it now, I'd even put it ahead of Mick Foley, it's THAT good.
I just finished the book a few days ago - it is a long read (540 pages), but it is compelling reading for any wrestling fans from the 80s/90s. As I understand it, he had more than 1500 pages written, but it needed to be whittled down. Here in Calgary, stacks of "Hitman" peer out from every bookstore in town. He's done a couple of book signings as well.
The book left me with an overwhelming sense that Bret still carries a lot of bitterness in him. I never realized how fucked up the whole Hart family was. The amount of in-fighting and jealousy really took its toll on their parents.
It is interesting, as cfgb mentions, how Bret definitely had a lot of admiration for Shawn Michaels early on, and you can see how that changes over the years into a full-on hatred.
With regard to his relationship with Vince, I got the sense that Bret is ambivalent on how he should feel about Vince. He doesn't doubt that Vince both made him and broke him as a wrestler.
If you do have the chance to get this book, I don't think you'll be disappointed. There's a lot on Davey, Anvil, Dynamite, Owen, Perfect and others.