I never thought a day might come when I would rate a Rowling book with only 1 star. I won't elaborate much about why I'm doing this, as many people have mentioned things I totally agree with in their reviews already. 
 Main points: 
 - I was NOT comparing this book to Harry Potter or expecting it to be anything magic/whodunit/politics or whatever else. My only expectation was that it would grip me by the throat and will not let go till the very end. Because that's what the Rowling I knew always did. 
 - The language, writing style, descriptions, sarcasm are very recognisably Rowling-ish; however, this is obviously not enough to keep the reader going. During the first 60 pages the reader has to get acquainted with a huge amount of characters, but nothing makes one care about them. Moreover, by the end of the 60 pages of introducing the characters I have already forgotten who were the people I've read about in the beginning. There are a lot of huge books (even bigger than this one) with an enormous amount of characters, but they are not introduced all at the same time making your head burst from seemingly useless information. 
 - Finally, unnecessary use of obscene language. Again, I've read books with description of sex acts, use of swearing, etc. etc., but it was always to the point. While in The Casual Vacancy it was always used out of the blue and for no reason. I mean, for example, do you really need to say that a guy's balls were full or that he had a boner in order to make the reader understand that this guy likes a particular girl? Is it really the only way? But Rowling does this constantly. As a fan and a reader I felt like the author kept lying to me over and over again. And the biggest lie was that in all her interviews she said that she doesn't really care about this book's reception because she's already famous and rich (and blah-blah-blah), so she just wrote the book she wanted to write. Well, that's the biggest lie ever. If I didn't know that Rowling is a well-educated woman, I would think that somebody mislead her into thinking that an adult novel means that you have to swear and mention sex every other page. But since I know that she is not stupid to think that, the only answer for me as to why she needed to do this is because she was afraid that people will not believe this is a book for adults, not a story for teenagers, unless she curses enough. 
 *Sigh* I thought I wouldn't write that much. I guess I am too disappointed to be silent about it. 
 And yes, I did not finish the book. I stopped at page 60-something. People say that after the first half it gets super-page-turning. Well, sorry, Rowling, life is too short to make yourself reading something so boring, insincere and forced even if it's written by your favourite author.