This is the first monograph biography of Gaetano Guadagni, author Patricia Howard has been working on Guadagni for years, and she's previously re-written the historic record on some essential stuff about him, like what his vocal range actually was, and the fact that his birthdate was wrong for years (this for whatever reason happens to castrati a lot) and that his birthname was actually Cosimo! So she's almost certainly the foremost expert on Gaetano Guadagni.
However that means she's published a lot of her Guadagni research already to get this reputation, and the book has that pesky recycled feeling. The information on his early life, acting, limited composing, puppetry, and relationship to the character of Orfeo has all been published before, which is maybe like 30-40% of the book. There's a lot of original stuff in here through, like the chapter on his work with Handel, which will likely prove to be the most heavily cited section because he's pretty hot right now, and a few tantalizing hints that Caffarelli might have given Guadagni a leg-up in his early career by getting him a gig in Lisbon which sheds a bit of a different angle on Caffarelli, as well as the whole "reform" singer/actor idea. As Caffarelli is known more for maltreating other singers, it could be a hint that at least one of the old timer recognized GG’s raw talent. But she unfortunately doesn't explore this idea much.
In general though she gets bogged down by facts and details and doesn't tell you what things "mean." For example, Gaetano Guadagni was a big puppet enthusiast in retirement and had a full marionette theater in his house which took up two whole rooms, and he gave free shows for the neighborhood kids and would apparently also ambush unsuspecting visitors to the town and make them sit through impromptu puppet shows. While of course this is just hilarious to think about by itself, Howard doesn't pull much meat out of it. She devotes a lot of words the history and details of late 18th century puppetry, which is all very interesting, but she seems to have forgotten to tell us what this love of puppetry might say about Gaetano Guadagni's personality and theatrical spirit.
Unfortunately I think somewhere along the line she also forgot that she was also supposed to be arguing for something in particular, which would be the title: why does Guadagni have the right to be called "the first modern castrato?" There’s a little bit tacked on the beginning and finish of the book about how he is the first "modern castrato," but otherwise it is not really mentioned in the book, and the term is not well defined. Maybe it was an after-thought when her editor said she needed a title?
I really hate to be a sourpuss about this book, because she's amassed an awful lot of original research on Guadagni's life, like an almost complete itinerary of where he was for just about every season he worked (and it’s actually really freaking hard to do that for opera singers), but I think the art of Doing History and Telling the Story got lost in the focus on verifying all sorts of little bits and bobs from his life. I've got my own ideas about who Guadagni was and what his legacy is this magnificent, ridiculous artform that we call opera, but they’re the same ideas I had before reading the book, and I’m not sure I could tell you what exactly the author thinks in that vein. Having read most of her research articles before, I was hoping she'd get into more of an overall synthesis on his life and legacy in longform, but I was left hungry. If this is your first time reading about Gaetano Guadagni you will probably get a lot more out of this.