I will try not to put any serious spoilers in this post...
Holy cow, this book sucks. Seriously. I enjoyed the previous ones. They were good stories, definitely pageturners. Not particularly brilliant prose, but told the tale fairly well. The books were well organized and the characters were pretty well fleshed out, which, given the increasing size and scale of the works, is no small feat.
But this book, on the other hand, seems thrown together. The sequence of narration seems arbitrary, as though Rowling occasionally got bored with the plot and decided to throw in 50 pages of reminiscing from one of the characters instead. The various problems and concerns of the characters have a totally haphazard feel to them, which negates the emotional tension they attempt to produce. It's not that there's too much going on - I wouldn't say that the plot is really that much more jampacked than the earlier books - it's just messy and far too dispersed. The attempt to create suspense by deferring full disclosure of information to the end of the text fails miserably, because there hasn't been enough information given early on to lead the reader to actually care.
Meanwhile, the didacticism of this work, the petty general moralizations, are so blunt that the plot comes to serve as a clumsy device to illustrate how important it is to be a good person. Except that rather than illustrating it, it just tells you over and over.
What I found most puzzling though, were all the veiled references to Nazism and German history. Sure, there's the obvious obsession with racial purity and requiring those with "alien" blood to register, but what about Nuremgard prison, or Durmstrang? Why do a little worldplay with a German Romantic movement? What kid is gonna get that? Shit, most adults won't. Yet I simply can't believe it's coincidental. Did Rowling think she was making the book more powerful, more monumental, by burying references to WWII in it?
In any case, sorry guys, but it's a stinker. Incidentally, the latest movie isn't so hot either. So much for Pottermania, eh?