As a book in itself, and as an end to the whole series... I think I feel good about it.
There were a few times when I definitely thought Rowling was going to go the Wild Bunch route (aka, "Rocks fall, everyone dies!!"). I'm actually glad she didn't, for reasons I can't adequately explain.
I am also glad to see that I was right, for once, about my one prediction for the book (i.e., that Harry's scar was a Horcrux. ...all right, technically, I said that his scar was the final Horcrux, but technicalities count).
At first, I thought that the book should have ended with Harry and Voldemort killing each other, that Harry's death ought to have been permanent, that his return from the afterlife was a little too much like Rowling having her cake and eating it too.
(Tangent: This reminds me of the old SNL sketch "Lothar of the Hill People": "You are indeed a fool! You would have your flagon of mead and drink it too!" "That statement is itself foolish! If I had a flagon of mead, would I not drink it?")
Upon second reflection, though... I think it fits with the internal logic of the story -- both within this book itself, and within the series as a whole. The source of evil in the Harry Potter books is the same source of evil that we see in Macbeth, in Faust, in Paradise Lost. Evil comes from a greed for power--oh, it may be a greed dressed up in a fig leaf of "The Greater Good" (about which more below), but sooner or later, it always comes down to wanting power for yourself. And wanting more power...and more...and more...and not caring who you trample under to get to it.
And I think that Harry getting to return from the dead... was a sort of reward for good-conduct on his part. That Harry deliberately renounced all attempts to increase his power for himself, that he even deliberately renounced all thoughts for his own continued survival...that, if you like, he accepted that the needs of the many outweighed the needs of the few or the one.
Harry Potter did not seek to conquer death for himself. And for that reason, he was able to.
(...and let's be honest here: Aslan and Gandalf got to come back; why not Harry?)
As for Dumbledore: We find out in this book the full extent of his sins and his flaws (though I think Rowling's been dropping hints throughout many, if not all, of the books that these flaws are there). We find him vain, selfish, pompous, and manipulative--treating people like dolls or puppets, moving them around to fulfill his own hidden goals. We find that Harry was just a cog in his own plans.
I should be absolutely livid at Dumbledore for this. I should hate him forever for being dishonest to Harry, for misleading him, for keeping him in the dark. And yet, I think this aspect of him makes him a lot more human, and a lot more sympathetic. People have talked a lot about Harry getting more and more mature and developed as the books have gone on...let us not forget that Dumbledore is getting more and more developed as well. Because Dumbledore is flawed...but here's the important part: He knows he is flawed. He admits to himself "Yes, what I did was wrong." And ever since his falling-out with Aberforth, he has tried to make amends.
(Compare Harry's last dialogue with Voldemort with Miles Vorkosigan's own thoughts during the interrogation of General Haroche at the end of Memory.)
And that's the difference between Dumbledore and Grindelwald, or Voldemort. And that's why I'm not angry at him, despite his flaws. The world is not divided into good wizards and Death Eaters--everybody in the book has bad parts to their characters, as do we all in real life.
As "For The Greater Good"... it's a phrase that has a sinister ring to it; as well it should, since it's the same phrase that's been used to justify a lot of really shitty things throughout history. But...there are times when the needs of the many do outweigh the needs of the one. The trick is distinguishing The Greater Good from your own personal desires-- or, if you prefer, making sure that you don't confuse what works for you with what everybody else should do. Grindelwald and Voldemort couldn't make that distinction; Dumbledore, at the close of things, could, even though he had to do some slightly unethical things to effect it.
As for the epilogue... you know what, to hell with it. It's basically the same way that The Return of the King ended, if you think about it. I give it a pass. And if you think that "They all got married and had lots of babies YAY" is a bad ending... well, I must say, you're going to be hella disappointed with a lot of books throughout history.
More to come in the next few days, probably, of a pointing-and-laughing nature, if the fans explode into a firestorm of rage on the Internet.