Last night I was at a friend's house and her five year old daughter told me that they were reading The Philosophers' Stone together. It was a shock to me, because I realised that yes, you could read the first book in the series to a five year old. Remember what it was like. Then think how inconceivable it would be to read Deathly Hallows to a child of that age. It made me realise how strong JKR's command of her material is, that each book develops naturally from the one before, but the development is inexorable. I can't think of any other book series which has attempted this, to change in maturity and tone to match the natural development of a child into an adult. There are many books and book series about that development, but few if any which embody it in their form.
I feel that this book shows that the success of the Harry Potter series is not a fluke, and that JKR is a better writer than I thought. Bloomsbury, and in a sense all the child readers, were gambling on her to carry it through. And nobody knew whether she could do it. A million orders were placed for what might have been an embarrassing mess. I think this shows that the success of the series is not because some random one of all the moderately talented writers out there got lucky, but because someone at Bloomsbury spotted an exceptional talent. Perhaps not a sentence-level talent, but something very special.
Don't get me wrong - there are some severe flaws in this book, and I think everyone would admit that the attempt to portray the soul-sapping boredom and aimlessness of the tent sequence was an embodiment too far. We don't need to be drifting in dreary tedium for quite that long. I'm not a massive fan of 'collect the plot tokens' fantasy either.
Overall though I thought it was confident and impressive. It is clear that the magic world is supposed to have had evil inherent, sleeping perhaps and sometimes overt, in its most venerable institutions and people. It only seemed wonderful and perfect to an 11 year old.
JKR said that she saw the start and end of the series before she began and I think this book proves it. I think the crux of the story is that coming to terms with death is what allows us to become full humans, and clinging to personal survival is what destroys us. But that death is real, and abuse and rape and torture are real, and we don't just come back from them. (I know the epilogue kind of contradicts that but that's just to comfort the smallest readers)