Interesting.....as the saying goes.
I liked the Potter books for the emotion and inventiveness of the stories. Rowling proved she has a knack for spinning tales. Her writing, on the other hand, was clunky, confusing, and downright hard to follow in many places....though she improved noticeably as the series went on. She wrecked the exposition with adverbs throughout...to a ludicrous level in some places. But the story lines and character arcs were very good overall.
The Casual Vacancy was a total dud for me. The writing seemed almost as bad as her early Potter efforts, and the story was just plain boring. One of those books with little to recommend. I might have been projecting my distaste for her sophomoric writing style...but I really expected some clever storylines. She seemed out to prove that she's a true "writer" and forgot her real strength in story-telling. There's a good reason it got universally panned.
Perhaps now she's back to form with story telling.