Mulling over this review made me realize that maybe 3 stars is an ungenerous vote. This book is certainly victim of a bad editing: it's full of repetitions (especially in the first part)which nobody bothered to remove and it makes a massive use brackets enclosing significant part of the text, and habit that, for my part, I strongly despise in novels. 
 Besides, I found Rowling's writing not as fluent as it used to be in previous works. Rowling's detractors have always accuse her since Harry Potter of being a bad writer because too wordy. I like this in her: I believe she knows her lexicon and her syntax and uses them to create well defined characters who, as I said for The Cuckoo's calling, turn out to be wonderfully Dickensian. Moreover, she takes her times in unfolding her plot, shying away from those rushed pacing that often characterize mystery novels but managing, at the same time, to keep her readers glued to the pages till the end. 
 The silkworm is no exception from this point of view but it can be denied (again, especially in the first part) that the author struggles to find her rhythm and every sentence seems to be over thought and artificial. 
 On the other hand, there are qualities in this book which put it a cut above the average mystery which usually hits the stands. Put in simple words Rowling is a writer with a heart: she builds characters and stories which are not just means to an end (a murder to be solved), she feels for them and makes you feel for them and uses them to convey social issues without sounding lecturing or paternalistic. From this point of view she is very "British": she is very concerned about social inequalities and, as already proven in Harry Potter, an advocate of the right to be different but in The silkworm there is no gratuitous melodrama nor she indulges in cheap tear-jerker stories. 
 Even if we can find some themes already present in her fantasy saga, this series is dedicated to adult readers and Rowling never forget them, so we shouldn't either. As much as she treated children with respect, so she does with her more mature audience: this is a mystery book and there is violence, blood and, in a limited way, sex and curses. There is real life, which Rowling proves she can manage brilliantly, with a touch of black humor but without thriving in the most gruesome or vulgar details. She can talk about removed guts without being excessively pulp (a genre that only few authors can afford) or plainly gross (a feat managed by many mystery authors) and she can have a transgender character between her protagonists without sounding sensationalistic or prudish but just, you know, a writer. 
 I also believe that with this book she got some things off her chest while describing a fictional literary world populated by egomaniac writers, victimized agents and petty publishers. It was fun reading about this, knowing that she knows this world in first person. 
 I have to say that the mystery was very well schemed but a couple of bog clues are blatantly said at the beginning of the story and inexplicably ignored by our investigator and this is a second reason why this book is rated less that its predecessor.