Here is a non-spoilery overview. I'm a great believer in structure over execution, and I think the structural strengths of this series of books are what the reader responds to, and this explains their success. It explains why the first book didn't hit as strongly as the second, and the third was the one where the series took off. I think this current book is best in the series, after 'Prisoner'.
I thought JKR had got self-conscious with success, but if so she seems to have shaken that off. And not only does the book integrate itself into the structure, but daringly subverts it in various interesting ways. I do recommend this book, so long as you understand it is a children's book, and the prose style is competent but not outstanding.
I don't think my brain is working so well at the moment. I'm taking ages to do sudoku and I didn't guess all the things that everyone else guessed. Like - who was the HBP and what does RAB stand for. Duh. I am stupid.
The only character in Harry Potter that I definitely would get it on with is Sirius Black. Still dead, alas, so that idea will have to be put on a back burner. But here's an interesting review from Ampersand (cuddly radical cartoonist blogger).
Professor Snape remains not only the best character in the series, but is one of the most interesting and complex characters in all of children's literature.
The books are not well written at the sentence level, and I think JKR sometimes sets up promising scenes, and then fluffs them in execution (sometimes she carries them off). However, I do think the premises are good, the underlying structural and character framework is exceptional. I think Snape is a good example - she consistently maintains the emotional ambiguity by which we are simultaneously convinced, against all the odds and all the evidence, that he is on the side of Good, while at the same time knowing that he is a Nasty Bastard. In this respect he is a much stronger and more interesting character than for example Dr House whose Secret Softy side shows a bit too readily.
Here's an interesting minor structural insight by another reader:
in alchemy, the philosopher’s stone is made through a system of refinement in which the stages are black, then white, then red - a fact that has been referred to in passing in the novels. In book 5, Black died; in book six, White died (”Albus” means “white”). If so, then Hagrid (whose name means “red”) is going to die in the next novel.
And what do you think of this comment, from yet another reader?
The horcrux was the potion, not the locket, and the reason Dumbledore was weakened and truly frightened was because he was fighting Voldemort for his soul and wasn’t sure he’d be able to finish his task in time…which was to die. He called Snape in specifically for that purpose.
Now that would be structurally satisfying.