A lot of people seem to think that Rowling rambled through three-quarters of the novel before realising she hadn't put any story into it, and then crammed it into the last quarter. I think that's a mistaken belief coming from a misunderstanding of how the world and characters of these books have evolved from Year One.
The first three books all had a kind of "Hardy Boys" feel to them; that Harry, Ron and Hermoine had a particular case to solve in each one, and that was the main focus of each book: The Case of the Philosopher's Stone, The Case of the Chamber of Secrets and The Case of the Prisoner of Azkaban.
However, from book four onwards the focus started to shift more and more to the ongoing story of Harry and Voldemort. What was back-story in the first three books became the main story for the rest of the series. The fact that Harry and Dumbledore don't begin the book's obligatory "adventure" until late in the book isn't a flaw, it is an indication that the books are no longer about the adventure, but about the bigger story of Harry's life.
And, of course, part of Harry's life is now romance. I'll agree that the romance in this book seemed a bit clunky and more than a little bit cliched, but I never thought J.K. Rowling was an exceptional wordsmith anyway. But, she gets the job done. She portrays the fact that Harry and his friends are growing up, and are having an awkward time dealing with a new set of feelings.
I think Harry's feelings for Ginny are particularly well described, in a way that I immediately could relate to. But Ron and Hermione's story, however, seemed rather poorly plotted, like some bad 80s teen romance movie. Especially with Ron getting with some random chick to make Hermione jealous - it's cliche-o-rama. I have to say, also, that these characters seem fairly naive for 16-year-olds. Whilst I'm sure that not all 16-year-olds are having the same kind of rampant sex that I was having at that age, the fact is that many of their peer group should be sexually active, and they therefore seem woefully immature. But, I guess we have to remind ourselves that this is aimed at a wide audience from a very early age, and perhaps young wizards and witches are more thoroughly protected from such nastiness as sex. Anyway, as I say, we get the general idea.
I scoff most heartily at any suggestion that the romance scenes were written into this book as a response, or a backlash, to slash and other fanfiction. Whilst I am sure that Rowling is aware of and, dare I suggest it, may even read fanfiction, I seriously doubt she gives it more than the attention it deserves. Fanfiction is at best a desperate attempt to make someone else's characters do what you want them to, and at worst a pitiful lack of original subject matter to write about. The fact is that Harry Potter and friends have been marching on into adolescence for some time now. Rowling added romance into these books, because that's what is important to a teenager and the absence of romance would have been even more noticable.
Anyway, I scanned a few messageboards and saw a few dingbats bewailing the death of the beloved Dumbledore, and crying foul of Rowling in a way reminiscent of Stephen King's Misery. Having thought about it, I realise that Dumbledore's death is absolutely vital for the success of the final chapter. Until now, Dumbledore has been Harry's safety net. Like Gandalf, the wizard he so resembles, Dumbledore always seems to come along at just the right time and save the day. Having such a saviour waiting in the wings would cheapen Harry's inevitable confrontation with Voldemort. We, like Harry, feel that he is safe as long as Dumbledore has his back. And that would remove much of the suspense of the final showdown.
Of course, Rowling has deliberately planted the seed in the reader's mind that Dumbledore may return from the dead. For instance, Dumbledore's close association with the Phoenix, and his certain trust in the man who killed him. Could Dumbledore really be dead if he so implicitly trusted his murderer? I think that bringing Dumbledore back from the grave would cheapen the message of the Harry Potter series; that being that people die and we have to learn to go on without them. It would cheapen the deaths of all those who were close to Harry. But, the fact that people are already speculating about a possible resurrection is in and of itself a selling point for the final book.
Of course, the ultimate question for me is whether or not Snape is truly evil. I think Rowling has done too much to build up this character as the nasty good guy to throw it all away now. Snape is such an interesting and conflicted character because he is one of the good guys, whilst having all the appearance of being one of the bad guys. And are we meant to just believe that after all of Dumbledore's protests that he trusts Snape completely, that Dumbledore was wrong?
I think there is far more to the story of Snape's apparent betrayal than meets the eye, which is going to make the next two years or so an excruciating wait. And that says more about how good these books are than anything.
One final thought on the relationship between Snape and Dumbledore, that I fear does not come from me, but comes from my darling Emily: Perhaps the reason that Dumbledore was so absolutely certain of Snape's loyalty was that Snape had made an Unbreakable Vow to Dumbledore.