One characteristic is the use of the local dialects and language quirks in the dialogues, which makes the story more immersive. The novels also tend to explore the social hierarchies of the time in New Orleans. The romances can be both sweet and full of obstacles, with the historical setting providing many of those challenges, like differences in social class or family feuds that are rooted in the city's past.
Well, they often have a vivid description of the unique architecture in New Orleans, like the beautiful French Quarter. The history, such as the Creole culture, is deeply embedded in the stories. And of course, there's always a passionate love story between the characters, with the backdrop of the city's rich history adding to the allure.