That's a big part, it's always good to pull your target audience in with somethign they can relate to.
They also benefited from being one of the few series in a long while that was styled and aimed for kids, but was intelligently written enough that adults could enjoy them. Not only does that expand the audience exponentially, but the kids will keep on liking the books as they get older.
For me, the single most satisfying element was the conherence of the world. Rowling started with one exception to the normal world, magic exists, and everythign else about the setting flowed from that. Particularly, she addressed the question of, "if magic exists, why don't we see it?". Her answer was the secrecy of the wizarding world and the various government agencies that make sure that magic stays hidden from us "muggles".
Good luck.
Yeah, I really agree with the first question.
The characters are so three dimensional, and so is the world, that I can't help but wonder if there really is a magic world that we don't know about. Rowling's made it believable. And I think what makes it alluring is different for everyone. I already gave you my answer.
But, hey, an opinion is an opinion.
That's a big part, it's always good to write books that have an interchangeable target audience. This series can be read by an eleven year old, but also a young adult, who although may understand more, still relates on the same level as the eleven year old.
The success is also due to the loyal fan base who kept the excitement coming. It seems every time this young Potter boy dies, another new discovery is made, giving the books a mysterious element.
The author of this series, not only had a beautiful knack for words, but she knew how not to give much away. Anyone reading, say, the fifth book is drawn to the sixth for the almost addicting desire to know what happens to the wizarding world.
The books had a plot line that could easily be followed, but is more in depth if you search. The series is written of problems many people face presented in humorous and adventurous ways. Particularly, she addressed the question of, "if magic exists, why don't we see it?". Her answer was the secrecy of the wizards world and the ministry, who always lets something slip.
i love the first answer you got! also i love knowing that J. K. Rowling has history and details for all of her characters. even though we don't find out everything it makes the characters seem more realistic when you know where they come from and their backgrounds. hope this helps!