A good reader makes predictions and thinks through the book as they read, evaluating what's happening and trying to place different key elements together. By the time "Deathy Hallows" is over, everything has fallen into place, and even the more boring elements of "Chamber of Secrets" is vital, since Rowling introduces the Horcruxes in "Half-Blood Prince" but, really, she introduced them all the way back in book two. Especially the Sword of Gryffindor, which is vital in the last two books. It's great to see how all the elements fit nicely into each other. They started off small and easy to read, and then they become these big, overstuffed stories that hurt my creative brain, wondering, how did she have all of this figured out?
Being a writer, myself, I get how the plot devices and characters fit all together. None of the stories I've even considered writing have that much going on, but the creative subconscious just creates and keeps creating this world, and all the pieces fit inside it and it all makes sense to the creator. Rowling probably was overwhelmed sometimes with how much all of pieces would work out. I'm sure she has notebooks filled with just connections and notes. If not, then her brain must be super-organized.
No wonder we haven't seen anything from her lately. She's probably still tapped out. It would be great to see another series of books from her, but her first seven books were a magnum opus, and therefore, I wouldn't care if she ever wrote another thing again. Nothing she would write again would probably hold a candle to the wind of Potter, and it would constantly be compared.
I guess that's the blessing and the curse of writing a modern classic. I can see this series living on for eons. But, since it's so great and so vast, and the world she created was so real, it's also the curse in which everything else will be judged, if she continues writing. I don't think that's what people intend to do, but the public has fallen in love with it so much, that they can't help wanting another set of Potter. They can't help comparing it, even if the next pieces she writes/publishes have nothing in common with it.