The only reason I started this series (I have #2 on audio) is because I thought Causal Vacancy was such a good novel.
I can understand why Rowling wanted to keep her authorship of this series a secret. I mean, there is the whole genre thing, it isn't a novel of society the same way Vacancy is - though there several critiques of society.
What it is - an above average British mystery.
While not quite following in the footsteps of Rendell and James, Rowling's mystery does remind a me a bit of them. Both Strike and Robin have that educated feeling of Rendell and James' detectives. There is a bit more humor here, than in James and Rendell - but the feeling is slightly similar.
Strike is called upon to investigate the apparent sucide of a top model - he's also in dealing with money issues. Robin, his temp, is not only working for him, but trying to find a job (or at the very least what she wants to do).
While the mystery is somewhat predictable towards the end, Rowling does look at race issues in a way that was never addressed in the Potter series. It's actually a pretty good mystery.