In modern fantasy fiction, there are essentially two prototypes of approach; that of Lord of the Rings and that of Narnia. Not that every work will copy one of these or be like one or the other or any other generalization that pedants will feel the need to scold me for, but that there's two basic, classic approaches to fantasy worlds.
The Narnian approach is simple, and usually followed by children's books. There's some hidden land of fantasy magic, it gets discovered, and you go on a fun tour through your imagination. It's almost an extended dream sequence. There's trolls and goblins and witches and elves and fairies and satyrs and... and it goes on. The magical creatures are there because they are magical creatures and this is a magical world. Nothing is really supposed to make sense, so much as present a fun escape from boring reality. The narrative space of the story is just a big bag for holding mythical creatures. It's fun. You're supposed to feel wonder at all the incredible surroundings, and not really think about why Medusa moved to New England and why no one has called the cops for missing persons.
It's pleasant, and there's nothing wrong with it.
The other approach was largely introduced by Tolkien, and that is of world-building. The author completely reinvents the world. Different continents, different history, different cultures, etc. If there are magical creatures, they were put in the mythical country when the ancient warlock Grumgould raised them to battle against the forces of light, they were driven underground by the king's armies, and the townsfolk still fear them. Point is, everything has a place, and is supposed to make sense, and is supposed to fit together. You are supposed to ask why Medusa moved to New England, because the author has a very clever backstory that he will introduce slowly and subtly throughout the books.
This is typically aimed more at adults, and is considered more sophisticated, probably because it can go wrong. It's supposed to make sense, and if it doesn't then it is bad.
Harry Potter is a terrible series because the author took the first type of fantasy and forced it to be the second type.
Basically, Harry Potter was first conceived as a children's book, and as such fits the Narnian mold perfectly. Harry learns he's a wizard, goes to a school full of wizards, and is filled with amazement and wonder at all the magic around him. There are ghosts in the school because ghosts are magical and the school is magical. The stairs move because they're magic stairs in a magic school. Centaurs live in the woods because they're magic in a magic woods in a magic school. Hogwarts is again just a big bag for holding magical stuff. It's not supposed to make sense. The reader, through the blank of Harry Potter, is supposed to escape and journey through strange things and meet strange creatures and have fun. If you smile while imagining a flying motorcycle, then the book has done its job.
If the series had stayed there, it would have been fine. It would have been a silly and fun story about love and courage and friendship.
But as the readership grew up, the author did something novel, which was she instead wrote later books for the 15-year-olds who read her first books when they were 10-year-olds. And it kept creeping up. Most of the people waiting in line for the later books were in college. Because the audience kept getting older, the novels tried to become more mature, and so ended up shoving Hogwarts in to a serious world-building-type fantasy where it was never intended to be.
It then invites serious fantasy readers to appraise Harry Potter at a deeper level, where it has no hope of standing.
That is why it is bad.
|College of Malicious Architecture|
Q: "Why do the stairs in the school move around?"
A: "Because they're magic stairs in a magic school."
Q: "But why did they make the stairs to purposefully inconvenience everyone inside the school? Why do they not magically stop the stairs from moving, and why did anyone ever make stairs to magically make kids late to class in the first place? That doesn't seem like an intelligible design feature in the top school in the world. It does absolutely no good and a great deal of bad. At the best, you can say the stairs are mildly annoying; but then considering how totally senseless their existence and operation and how much easier it would be to not have moving stairs, it really seems like the stairs were an intentionally malicious invention. Who made them, why did he do this in the first place, did he get fired, why haven't they fixed it?"
That's just the stairs. That's just one page of the first book. A single simple example that I made up while writing this. I could list a dozen more things, but I will stick to the stairs.
Now, the first book was a kids' book and the stairs move because it's fun. And maybe it isn't fair to apply an adult-book lens to the first books. But the stairs still move in later books! Because they moved in the first book. And that isn't even the problem! If some brilliant wizard decides to fix the stairs in place in a later book, the later book is an adult book, and so is supposed to present a consistent history to everything. What reason is given for the wizard doing that now and only now? Why didn't the wizard do that twenty years ago, before the events of the story? Why (in the later book) did they build these stupid stairs at all?
That's why it's bad. She made a world where she didn't have to make sense, so it didn't. Then she tried to force the world to make sense, and it still doesn't. She removed the "it's for children" excuse she rightfully had at first, and was left with a world of characters who have no conception of their own universe. The masters of the school have first years late to class the entire first month every year because of moving stairs and never bother to think "wait a minute... there's no reason for stairs to move at all!"
For more trashing of Harry Potter, please see the links below:
The Sorting Hat is a Jerk
Harry Potter and the Sorcerers Who Don't Understand Magic
Harry Potter and the Council of Rejects
Actually, the World is Split in to Good People and Death Eaters
The Ending that Would Have Made Harry Potter