Over the past several months I have read aloud the whole Harry Potter series.
It was a wholly enjoyable experience, and confirmed my opinion of the excellence of these books.
(Which is, itself, a revised opinion: I found the early books uninteresting at the time they were published - and it was only after I had been given 'the key' by reading the later parts of the last book that I was able to go back and appreciate the earlier ones. I pretty much first-read the books in reverse order.)
My general impression about quality is that Philosophers Stone and Chamber make up a duo of 'perfect' children's books in which the deeper meanings are only hinted at briefly - but they are certainly present. Azkaban is the teen-novel transition - and also perfect of its kind. I now perceive a sagging in the middle with Goblet and Phoenix, in each volume of which there is some (but not much) 'surplus fat'. And Prince and Hallows become fully adult novels, and make up a single unit, with the quality of writing taking a qualitative step up.
Rowling's main limitation as a writer, aside from the need for better sub-editing - which would tidy-up the writing but not really improve the book; is that the quality of prose writing - while perfectly effective - is not as good as the best of the Fantasy genre (e.g. Tolkien, Lewis, Ray Bradbury).
A second problem is that the author's inventiveness with respect to magical possibilities makes it impossible for her to be consistent. The clearest example is the Time Turner, which is much too powerful a device.
Another example is apparation. Or the ability of wizards to become invisible (either with cloaks or disillusionment charms - no wizard would ever know if they were alone/ unobserved).
Or the Polyjuice potion and Imperius Curse (you could never be sure who you were talking-to, or whether they were responsible for their actions). But in general, she cannot keep the magic fully under control.
Also, the big 'set-pieces' do not work very well for me. For example, the episodes when the trio break into the Ministry of Magic and Gringotts are the only parts of Hallows which are not wholly-successful and absorbing. And the descriptions of battles and duels are contrived, especially by comparison with those of ex-soldiers such as Tolkien, Lewis, or Lloyd Alexander. The tasks in Goblet are unconvincing too.
But this is the price to pay for such richness of ideas - and I can happily suspend my critical faculties most of the time.
As more-then-compensation there is a deep underlying spiritual (indeed Christian) dimension concerning death, a profound meditation upon love, and some gripping character studies in Harry, Snape, Dumbledore, Herminone, Ron, Luna and Neville (plus a terrific supporting cast).
There is a really enjoyable humour throughout - not just jokes, but comedy in its ancient sense of the play of humours, character.
And the detail is wonderful - the detailed descriptions of daily life at school, having meals, doing homework etc.
Yet the biggest virtue of all is the emotional punch of the Deathly Hallows.
I found it harder to read out the Deathly Hallows without breaking down and blubbing, than any other book I have ever read aloud.
That, I think, is a tribute to the author!
Any one of these great emotional climaxes comes in the following passage:
Snape, talking to Dumbeldore about Harry: You have kept him alive so that he can die at the right moment? ... I have spied for you, and lied for you, put myself in mortal danger for you. Everything was supposed to be to keep Lily Potter's son safe. Now you tell me that you have been raising him like a pig for slaughter?
In context, including what follows, this is so moving that we tend to assume it is true, but it is not.
On reflection, we recall that Dumbledore only understood about Horcruxes, and that Harry's scar was a Horcrux, in the last few months of his life - so he could not have raised Harry with this in mind.
On the other hand, what does become clear is that Dumbedore's love for Harry is less than his determination to rid the world of Voldemort - and this is shocking enough, albeit morally less repellent or perhaps even admirable (and Dumbeldore was not asking of Harry more than he was himself prepared to give).
As a final aside - I was struck by how often, and how readily, Harry lied all throughout the series of books, and without any strong sense that lying was wrong.
I suspect that this may be a male female difference - since I don't recall heroic and good characters in similarly Christian books by men who have Harry's, ummm, instrumental attitude to verbal veracity.
Or perhaps this is more like the attitude of the pagan saga-men for whom successful deception was a virtue, when deployed in a good cause (ie. for the home team).
At any rate, only after his sanctification by death and rebirth, and in the final pages of the series, does Harry become wholly truthful - final recognition that truth is indeed among the highest values.