A lot of people compare Dark Places to Gone Girl and say, book-wise, Gone Girl was the better book. I actually liked Dark Places better, so when I found out they were making it into a movie, I was of course skeptical about whether or not it'd be good. I just finished watching it and was happy that my skepticism was for naught - this movie stayed true to the book. Casting was done well and the flow proved that the screenplay writers & director paid attention to the original book.
The book is dark, has some twists and turns and doesn't gloss over anything. Where in Gone Girl I felt like some scenes were made a little lighter for the screen, Dark Places doesn't have that issue. The sets were also very accurate - it's been YEARS since I read the book, but while watching the movie everything came back to me...the layout of the farm house, the crappy apartment Libby lived in as an adult with her collection of stolen items...all the way down to crap hole Runner was living in...
This is not going to be a big blockbuster. Most people will not like it (as you can tell by the ratings) but I will tell you, if you like thrillers/mysteries with twists and turns then watch it. If you've read the book, watch it. It's not the greatest movie ever done, but it was good enough that I felt compelled to write my first IMDb review.
And even if you don't watch the movie, read the book. If you like Patterson, Demille or Clancy, you'll like Dark Places.