Can't imagine what. They're quite well-written. Strike is an interesting, multi-layered protagonist, the pacing and dialogue are cracking, and the mysteries are actual mysteries. I'm not much of a mystery fan, but these kept me engaged throughout the book and actually surprised me at the end without stupid 'twists' that are unsupported by the narrative (a big problem with modern mysteries and crime fiction).
Sometimes I think these criticisms come from a healthy dose of envy toward a successful writer, a need to 'take them down a peg'. Rowling's early Potter books are certainly weaker than her later books, but as she polished her craft her tremendous skills at characterization and pacing are undeniable. I personally really disliked
The Casual Vacancy, but that was a matter of taste (I'm tremendously bored by 'well-off white people behaving badly and full of ennui' books) not the author's talent.
Still, to each his own
There are plenty of bookfish in the literary sea, enough for anyone's taste.
