This is not a book where the plot is particularly important. The characters are the driving force, and there are a great number of them, all well developed and fully realised. It took me a while to work out who was who (something that has guaranteed me at least a second read, if not a third and a fourth) but once the generic names have all been sorted into their respective lives, the book becomes - for lack of a better word - an absolute delight to read. Yes, it can be harsh, cruel, depressing, heartbreaking. There are characters with no good points to be found (Howard and Simon are the two I'm thinking of here) and even the most likeable of characters have weakness and unlikable traits. However, the "delight" here comes from the satisfaction of reading damn good writing. It is a book about real people, real life. I know people who are very like a lot of these characters, though the quaint English setting is not one I'm familiar with.
The writing itself, something I believe Rowling has been criticised for in the past, is easy to read, non-intrusive and even subtly poetic at times. Any swearing or unpleasant description fits perfectly into the story, without becoming a distraction. The tone of the book is clearly set in the first three pages - the last lines of the first chapter are: "Barry was lying motionless and unresponsive on the ground in a pool of his own vomit; Mary was crouching beside him, the knees of her tights ripped, clutching his hand, sobbing and whispering his name."
One criticism of the book that I've noticed is people saying they were bored, and/or unmoved by the characters. I quite honestly cannot see how this is possible. The writing carries along the story so well that I couldn't put it down, and though not a lot happens in terms of plot, the characters are so fascinating that this is completely irrelevant. It is a character study at heart, and those expecting otherwise should not lower their expectations but rather suspend them.
There were moments in The Casual Vacancy where I was moved to tears (Krystal, Robbie); where anger and hatred for a certain character (Simon, Obbo) left me feeling ill and genuinely vengeful; where I felt such pity for the weak pathetic lives of some (Sam, "Cubby", Terri) that I was glad they existed only on paper and did not have to endure their miserable existence for real. There were characters I wanted to slap, either because they were so awful (Howard, Gavin) or so lovely but stupid (Ruth); there were also characters I wish could have been included more - mainly Patricia, though there were others of interest.
My only advice when reading this is to go in with no expectations. Ignore who wrote it and focus on it as an entirely separate entity from the Rowling empire, at least until you've finished it. It deserves this much and more. The Casual Vacancy proves once and for all that Rowling is no one-trick-pony.