I mean, yeah, I don't know how else to rate this. It's on a totally different scale than a novel or whatever. If you are interested in musical theater in general and in Sondheim in particular then obviously this book is for you. But also if you are interested in learning more about how a writer who is EXTREMELY GOOD at what he does actually does what he does, you might want to look at this. There is tons of good writing advice packed in here, and a lot of fascinating critical self-dissection along the lines of that Community post-mortem Dan Harmon did in the AV Club. There are a bunch of parts where Sondheim points out egregious errors in his work. In time-honored and universally-cherished songs! Songs you love and know by heart! And he points out problems you probably never even noticed and will now not be able to unsee! But for every "I never should have done that and I can't believe that at the time I couldn't think of a better way to finish that line" moment there is a moment where he points to something and says "See what I did there? That's *really good*". And it's great. It's totally entertaining and fascinating and useful.
Overall this is a great lesson in the importance of constraints in writing. Because man does he have to work with constraints. It has to not only make sense, but it has to rhyme. (And the part at the beginning where he talks about the different kinds of rhyme, and why only perfect rhymes matter, was fascinating, and made me want to re-evaluate the lyrics of songwriters who we consider to be "really good lyricists". Because maybe there is a lost-art thing happening there in popular music? Maybe?)
AND also about constraints, there are a number of examples where some of the best songs of his career were 3rd or 4th drafts, or last-minute additions to the show, written in hotel rooms in Boston. The show wasn't working, he needed to fix it. It's not done until it's done. The amount of cut songs in here is mind-blowing. He just writes and writes and writes and keeps going until it's done, and then still keeps going after it's done. It's really inspiring.
I haven't read the whole book, I'm skipping around from show to show and enjoying it, but this was at 5 stars after the first few sections I read (Company & A Little Night Music, in my case).
Really really looking forward to the 2nd volume of this, so we can dig into Assassins and the second acts of Sunday In the Park With George and Into the Woods, about which I have Opinions, so I cannot wait to see how they mesh and clash with His opinions.