Suskin compiles articles from newspapers, from chapters of biographies, anyplace he could fine an in-the-know first person account from someone close to a Broadway musical that bombed. He adds a few of his own annotations when the original author doesn't quite get things right or a bit of historical context will make the old essay work more comprehensible to modern readers.
I think if I had read four or five of these accounts, I would have given the book one more star, as the essays are quite enlightening about all of the things that can go wrong inside a production, about how difficult it can be to maintain perspective and know that one is putting time, money and effort into a hopeless cause. I was quite entertained for the first hundred pages or so. But I read the whole book, and after a while, the stories seemed too repetitive.
Also, since these productions all flopped, even a big Broadway fan like myself doesn't know that much about them. I know the reputations of many of the producers, directors, writers, and actors who were attached, but ultimately I don't know these shows and really can't know them as there aren't filmed versions and failed productions are rarely revived. That makes all of this hard to grasp in the end: how bad was it? Which of these might have succeeded in another context. We don't know and can't ever know.
Finally, the book would be more entertaining if more of the flops in question were more recent, but very few are. Almost all of them happened before 1980. That's a big historical gap that leaves one wondering while all the failures of the last thirty years aren't represented. They'd be more interesting to read about.