I think part of the reason why Harry Potter is so amazing is because there's so many little details to it. In most stories they just tell you about the main characters and give you a few descriptions of their house, but with Harry Potter you have this whole mental map of the castle in your head and you know all about the non-important side characters. You even know what other characters' parents are like, and all of their backstories. You know all about the wizarding world and society and all of their laws, and Jo tells you all about characters who are never even in the books. She didn't just tell a story, she created an entire world. She's so incredibly talented, it's amazing.