One author who excels at putting heart and soul (and a lot of humor) into fantasy and mystery is JK Rowling. Her third book in the Cormoran Strike mystery series, Career of Evil, is a truly excellent book. It clocks it at about 500 pages; I was at the tail end of a very slow reading year, and yet I managed to plow through the book in only a few days. I even stayed up quite late one weeknight to finish it, which is rare for me.
What made this book so good? I mean, yes, there's the whole serial-killer-who-seems-to-have-a-personal-vendetta-against-Strike plot, and that is very compelling to read. But the mystery portion of a mystery novel is, strangely, never the reason I fall in love with the story. I spend zero time trying to figure out whodunnit while I'm reading the story (possibly because I almost always skip ahead to the end before I finish the second chapter, but even then, I don't really look for clues while reading the rest of the book).
Really, what made this book for me is that Rowling/Galbraith finally delivered on the Robin Ellacott part of the story. For the first two books in the series, I really loved Robin as a character - she is strong, kind, loyal and brave - but I hated her fiancee. I still hate her fiancee, but I understand better now why Robin stayed with him. We learn much more about Robin in this outing, spend much more time in her head. I think Robin is where the link to the Harry Potter stories is the strongest in this series (if you happen to be looking for a link). She is exactly the sort of person Hermione Granger would grow up to be. And, as you may know, Hermione didn't have the best taste in men, either.
Another plus in this novel's column is that Strike's ex-girlfriend Charlotte gets hardly any mention. Charlotte was the worst, and I bid her good riddance. I hope she doesn't return, though that is probably asking too much. Why both main characters have so much melodrama in their romantic relationships is beyond me. Much as we learned about Robin in this book, we also learned quite a bit about Cormoran Strike's formative years, and I was a glutton for the information. Career of Evil was like birthday cake for me. While I think Strike is coming out to be more of a loner and isolationist than I would have liked, he's still a very interesting person to spend 500 pages with. I just wish he didn't so easily dispose of women.
Of course, when you have a man and a woman with melodramatic romances in their lives, it's inevitable that there would be sexual tension between them. And there is, certainly, between Robin and Strike. It's been building up for three books now, and I'm not sure where it's going or what will happen. But I assume Rowling/Galbraith knows, and I trust her completely.
The Cormoran Strike (I admit it irks me that the series is named only after Strike and does not mention Robin at all) mystery series absolutely does not fall into the "cozy" subgenre. They are bloody, dark, and very complicated stories. But they're also very well-written, and the series improves with each book, so I highly recommend checking them out if you have any interest. Especially for Robin - it's very difficult not to love her.