Casual Vacancy was a big depart from Harry Potter. Aside from being geared toward an adult readership, it's a completely different genre - "slice of life" rather than fantasy. It tells the story of Pagford, a small town in the English countryside, in the wake of a city council member's death. All stories come back, in one way or another, to that empty council seat and what it means to the lives of the town's residents - from its wealthier members right down to the poorest. 
 A big part of the magic of Harry Potter was the way in which Rowling created a world of stereotype characters - easily grasped and understood at a glance - then remained in their space until they started to come alive. And yet, strangely, they remained stereotypes, just stereotypes that we came to know and to care for. 
 In Casual Vacancy, she does the same thing. We have the lower class girl with the turbulent home life, and we have the teen obsessed with living "authentically", the over-achieving "tiger mom" immigrant who had a sort of arranged marriage, the social worker struggling with professional boundaries, the bored housewife fantasising about a singer in her daughter's favourite boy band, etc. 
 Each of these characters is and remains a stock. Rarely do they have traits that are not perfectly in keeping with their "type." And, yet, we stay with them, we watch them, and over 500 pages, sheer time and care fills them out and makes them whole. 
 It's a remarkable process. 
 Harry Potter had its horror and tragedy, but Casual Vacancy lacks its hope. The characters are petty and locked into their own experiences. They are hurt, and they respond by lashing out in a great web of misery. Worse, there is little resolution. Most characters end in the same position - or worse - as they started, or have only just set a course for possible change that is well beyond the scope of this book. It doesn't revel in the pain, and it does have its moments of levity, but it's easy to see how this might be a difficult read for some. 
 One similarity between the two works that interested me is how both Harry Potter and Casual Vacancy work as representations of tyrants and how people deal with/react to them. In Harry Potter, the theme is placed in a fantasy setting, and the tyrant is defeated through valiance and friendship. In Casual Vacancy, however, things are a little bleaker. (view spoiler)[And while the tyrant is eventually defeated, it is through the failure of his own body - a realistic fluke that offers that dim ray of hope to the town. (hide spoiler)] 
 I doubt that I would have picked up this book if not for the author, and it's easy to see why so many people were disappointed with it. It's clearly Rowling's writing, but this is something completely different, and marketing the book as "by the author of Harry Potter" does it a disservice. That said, it's a solid piece of writing. Rowling did a great job showing us the complex web of small town life, and navigating between such a large cast of characters in a way that kept it interesting (in the sense that adult "slice of life" fiction is interesting - obviously not a genre for everyone!).