They're appealing because they offer a unique blend of mystery and the supernatural. Readers get to experience the thrill of a detective story while also being immersed in a world of magic, ghosts, and other paranormal elements.
Another great one is 'The Rivers of London' by Ben Aaronovitch. It features Peter Grant, a police constable who discovers he has magical abilities and uses them to solve crimes with a paranormal twist in London.
Another important theme is the struggle between good and evil in the paranormal context. There are malevolent forces in this hidden world that pose threats to the normal world, and the detective has to fight against them to maintain the balance. This involves not only physical battles but also moral dilemmas as he has to make choices about how to deal with different paranormal entities.
Often, they start with a mystery that seems to have a paranormal origin. For example, a strange death that has no normal explanation. Then the detective character, who may or may not have some paranormal abilities themselves, starts to investigate. As they dig deeper, they meet other characters, some of whom they may develop romantic feelings for. And the plot develops as they try to solve the mystery while dealing with their growing relationships.
The blend of the paranormal and detective elements. In these novels, you get to see detectives use both their regular investigative skills and deal with the supernatural. For example, in 'The Dresden Files', Harry Dresden has to use his knowledge of magic and the magical community to solve crimes that the normal police can't even begin to understand.
Peter Grant is a very popular character. He is the main detective in the series. He is unique as he is a police constable who also has the ability to see and interact with the paranormal world, which makes him a perfect fit for solving the strange cases that involve magic and other supernatural elements.
One popular one could be 'The Hollows' series which features a witch as a main character in a world full of paranormal elements and detective - like investigations. It has elements of mystery, magic, and a unique take on the supernatural world.
Well, in some of these novels, you might have a witch protagonist like Rachel Morgan. She's often a strong - willed character with magical abilities and a knack for getting into trouble and then using her skills to get out of it, much like a detective would. She has to deal with all sorts of paranormal beings in her world.