I did not understand why, because this book is in some great ways. The characters are very successful anti-hero, intrigue and suspense are very good.
The style, psychology, construction is superb. The author alternates two views. The first, almost in real time, recounts the day before the terrible carnage of a family from the perspective of the alleged perpetrator, the eldest son sentenced to life imprisonment. The other takes place 24 years later, it is a kind of involuntary investigation by Libby, the girl who survived the massacre of his family without ever being really recovered. It's very clever, often funny, sometimes brilliant. Libby is a character of very high caliber.
The conclusion is very successful, logical, believable.
Gillian Flynn is really very gifted, but several issues prevented me from plunging completely in his book.
The building is indeed very beautiful, but much ax the pace of reading. Moreover the text is very rich, full of asides often very fair, without direct contact with the plot. I did not count the times I found myself daydreaming instead of reading. This is not necessarily a fault, certainly, but as part of a thriller this affects the voltage and the reader's attention.
I also blame the author's penchant for systematic and coarse sordid, sometimes sordid and often free. I found it very artificial, very diligent, monochrome. Everything is dirty, everything is ugly, everything is sad. That in which the book's title is all but lie. At times, I thought I read Thomas Hardy's Jude the Obscure like!
Finally the characters are a bit too "written" to be totally credible. They are all built on the same mold: each must have its default, its fault, its share of malice or cowardice. Again the bias of the author has very artificial resonances, its characters are like guided, it sounds wrong, it lacks humanity.
To me The Dark Places is a good book, sometimes a very good book, but too chopped, too padlocked too mastered, too artificial to be truly great book he could have been.
