On The PotterSarah has asked my opinion on Harry Potter and the Order of the Phoenix, and I thought I'd chime in. I'll try my best to keep it spoiler-free, but if you're waiting to read the book, you might want to skip this entry.
Sarah feels like the book's not well enough edited (could be lots shorter), and that Harry needs a good smack upside the head. As for the editing, I didn't see too many problems, but then I didn't read it from an editing standpoint, so it's possible I could have missed a few things. I certainly didn't feel the "jeez, this is going on too long" or "she could have said that in half the length" feelings, though. I suppose I'm one of those people who could read Rowling day in and day out: I was hating making progress through the book, because every page down was a page I couldn't look forward to any more. What can I say? I'm a fanboy -- I like her writing "voice." :-)
As for Harry being insufferable, well, try being fifteen and male sometime. That's the way it works. For that matter, I liked Harry passionate and hair-triggered; for a guy who's been through as much trouble and familial humiliation as he has, it was getting old that he took everything nobly and in stride. I was surprised that Rowling wrote Ron and Hermione mature enough to stand fast in the face of Harry's freak-outs, though; that might be the only believability chink in her characters' armor.
Put simply, I liked it. But, bummer: we've got to wait another year (or two, or three) for the next, and the series is scheduled to end after only two more books!