Encouraged by
The Cuckoo's Calling I charged right into this one for which Rowling declined to hide behind a nom de plume. She narrates well, I kept reading all the way to the end, but this is depressing enough to have been Russian.
It also has a few technical problems. First of all, there are no particularly likeable characters. Maybe the guy who dies in the first chapter would have been a good guy, but, as noted, he dies in the first chapter. Second, there are lots of characters and it was never clear to me which were central. Omniscience on the part of the author is all well and good, but when we are set to wandering around in the thought processes of a dozen or so characters, it can be difficult to follow the thread, assuming there is one - a point I am not willing to concede.
Third, and this is a problem which I have noted before although probably not in this setting, she is very dependent on phonetic representation of dialect, thus rendering much of the dialogue unintelligible to the average reader, certainly to the American reader - although I suspect it makes rough going for many British readers as well. It is also a problem in much of Mark Twain's writing although there the purpose was humor, and here it is to emphasize class distinctions (I think). I continually had to stop and sound out the letter groups on the page and still frequently could only guess from context what was being said.
Finally, the plot is amorphous at best. The title addresses a peculiarity of British local government. When someone dies in office, the result is known as a "casual vacancy." The guy who dies in the beginning was a councilman and the title, at least, refers to the seat left vacant and the candidates and electoral malfeasance surrounding the filling of the position.
The whole business is curiously unsatisfying. I suspect the idea was to show all the characters through their associations with and feelings about the dead guy. And - feel free to show me the error of my thinking - it doesn't quite come off.