At more than 900 pages and over 30 hours of audiobook (which is how I completed it), "Troubled Blood" involves quite a commitment, but repays that commitment with a twisting, turning narrative that never flags.
Some of the length can be attributed to a considerable amount of backstory, which might come across as padding to existing fans of the Cormoran Strike series, but is invaluable to new readers. I suspect Rowling (the author behind the Galbraith pseudonym) anticipated that this book would attract new readers to the series. Certainly it did me.
The book is long, but it is not slow-paced or languorous in any way. What I would describe it as is: painstaking. This is not the hour-long TV episode of a cold case investigation. The reader follows Strike and his partner Robin Ellacott through a dogged pursuit of leads, dead ends, long-dead witnesses and broken lives, which feels more realistic than than tied-up-in-an-hour TV episodes. And it is a testament to Rowling/Galbraith's skill as a writer that this painstaking investigation holds the reader's interest through many hours.
No doubt everyone has thrashed over the "controversy" about the book, which was a total beat-up generated by a misleading review in a right-wing newspaper. But once more for those in the back row: THIS BOOK IS NOT TRANSPHOBIC. There are no trans characters in the book. The serial killer originally assumed to be the murderer of the missing woman was not trans and was not even a cross-dresser. He seems to have occasionally used disguises or put on a false "camp" persona to put his victims at ease, thinking he was harmless. If this character makes you think of trans women, YOU are the transphobe.
That said, Rowling has clearly laced this book with a number of details that hint at her disapproval of "woke" ideas about gender and politics more generally (along with her disapproval of Scottish nationalism, which is if anything even more blatant in the text). For a start, in a book where almost every character is three-dimensional and in some way flawed, the only characters that come across wholly positively are the daughter of the missing woman and the daughter's female partner. As anyone who has watched the UK gender debates for any period of time will realise, many proponents of gender identity would infer a pro-lesbian message (especially one that was completely inessential to the plot, which this is) as being an anti-trans "dog whistle", so it doesn't surprise me that Rowling is still being denounced for this book despite the complete silence on anything to do with transgender people. Even more blatant, though, are the multiple points in the plot where Rowling is clearly mocking the idea that "sex work is [just] work". Whether it's the entitled, self-absorbed young students who impose on Robyn and her flatmate while en route to a "Slut Walk" protest, or the elderly former prostitute mocking a past social worker who had adhered to the "sex work is work" idea, these episodes are also "dog whistles" by Rowling registering disapproval of woke views. (The more obnoxious of the students is even a male with a beard, which is basically a trope for woke Social Justice Warriors.)
Running through the whole book, especially the parts written from Robin Ellacott's point of view, is a painstaking evisceration of how some men treat women extremely badly. From the murders by the serial killer Creek, to the casual dehumanisation perpetrated by many of the other male characters, "Troubled Blood" is replete with episodes showing what women encounter and, often, put up with. This, too, will probably be none-too-pleasing for those who have denounced the book.
In short: if you like carefully plotted, intricate murder mysteries, you will enjoy this book. If your identity is bound up in social justice and gender identity, you will probably notice that the author is ever so delicately having a go at your views, and you will hate it.
Either way, I will bet you won't work out who the real killer is until the very end.
(Edited to add Robin Ellacott's first name now that I've gone back to check if it was Robin or Robyn. Problem with only using the audiobook version!)