I'm always surprised when people describe the books as simplistic or childish. I grew up with the books, and was the same age as Harry by the time Deathly Hallows came out, and my sentimental attachment to them is enormous, but I know no shortage of discerning adults who think the books are wonderful, compelling, reading, and I tend to wonder whether the people who see them as childish and simplistic read past the second book, because the later books in particular deal with some genuinely complex emotional and moral stuff, questions of injustice, shifting friendships and family relationships, of what it really means to be brave and good as opposed to what it means to take the easy route that looks like bravery and goodness. The characterisations are rich and layered for the leads and far from two-dimensional for secondary characters, though you need to be actively looking to see that sometimes (there are personality things you might miss when reading as a younger kid but see clearly on a reread when you're older), and Rowling writes with a great ear for dialogue and a mystery writer's enthusiasm for clue-planting and careful plotting.
(We didn't have midnight releases here - we had 9am ones instead for the later books, when they were being strictly rolled out at the same time everywhere around the world - and I was there at 8.59 counting down for the 6th book, and got there shortly after the shop opening for the 7th.)
