I found utterly unreadable. But it was not the simple idea that she'd tried something different that put me off, and so I was willing to give her another chance with The Cuckoo's Calling.
This book was published under a pseudonym, Robert Galbraith. As is so often the case when big writers try using a pen name, her secret was quickly exposed. We'll never know if the book would have been commercially successful on its own merits, but we can still judge its artistic merits.
I do credit Rowling for committing wholly to the pen name; The Cuckoo's Calling doesn't feel at all like the books she's written before. As Robert Galbraith, she jumped into the "hard-boiled detective" genre, creating a curmudgeonly war veteran named Cormoran Strike and leaning into many of the conventions of the format (albeit through a Londoner's lens). This book has her detective hired by a wealthy man who refuses to believe that his sister -- a famous supermodel -- committed suicide. He wants Strike to prove it was murder.
I found the book to be intermittently successful. The two main characters, Strike and his temporary secretary Robin, are both fairly interesting individuals. The blend of their oh-so-British mannerisms with the oh-so-traditional trappings of private detective fiction feels like something both familiar and unusual. Robin is particularly intriguing, seeing her struggle between the feeling that she shouldn't get caught up in this world, and the simple fact that she loves it.
But the book is, quite simply, far too long for the genre. It may have been published under the name Robert Galbraith, but one senses the editor knew this was really the work of J.K. Rowling... and was too timid to insist on some sorely needed edits. Sure, a web of possible suspects is the bread and butter of a good mystery. But The Cuckoo's Calling is easily twice as long as the average detective novel, and really begins to feel the strain of that length long before the final chapter. The sheer number of red herrings becomes tedious.
And ultimately, the ending is pretty terrible. I was sort of circling the "solution" to the mystery around the halfway point, but I dismissed it out of hand, thinking "it couldn't possibly be that, because that doesn't make any sense!" And yet that was indeed the ending. And indeed it didn't make any sense.
The Cuckoo's Calling is a far better effort than The Casual Vacancy, to be sure. But even though it was the first of a series of Cormoran Strike novels, I don't really think I enjoyed it enough to investigate the next one. I give the novel a B-.