Remember when I said that I wasn't going to re-read this book until after the movie came out? Yeah, I lied. I do that a lot. But, come on, the thing was $3 at a used-book store and I couldn't resist.
I think I've said enough about the series in my reviews of the other books (here, here, here, here) to go over it all again. Long story short: Formulaic but almost always enjoyable; good, fun characters and progressively more interesting stories; flawed, but never boring.
That being said, Deathly Hallows is by far the most mature and the darkest book of the series. Our three heroes are on their own as they decide to not return to Hogwarts and spend all their time trying to find and destroy the Horcruxes left behind by Voldemort. They have almost no information to go on, so there's a lot of guesswork and, as usual with Harry Potter, a lot of incredibly lucky coincidences. We're also introduced to a new mystery, that of the Deathly Hallows, which seems to be related to the main quest but isn't really important until the very end.
The best thing about the book is the way that Rowling manages to convey to us just how alone and isolated the kids are this time around. Before, Harry always had adults to rely on when things got dicey. This time around, however, the trio really must rely on what little experience they have (and Hermione's genius), and sometimes their plans go terribly wrong. They're still just teenagers, after all. They have volatile tempers and moments of silliness, all while being quite justifiably terrified and lonely. There are moments when things get downright horrifying-- the trip to Godric's Hollow is a brilliantly told episode right out of a horror story.
The biggest problem for me is the pacing of the story. Rowling has set up a great, complicated, dark mystery for the readers, and for once she is completely free to break away from the well-known formula, just by taking the kids out of Hogwarts. But she wastes the opportunity to do so. Instead, we have the same exhausted formula as with the other books: one long period of mystery and dead-ends, and all the revelations are crammed in at the end of the school year. I understand the logic behind it (they have little time as they progress, etc), but the last fourth of the book just feels terribly rushed. You get used to the slow but comfortable pace of the camping and investigation, and then BLAM! Suddenly you're thrown into an 150mph dive where you get no time to breathe, only a barrage of exposition and information that's just hard to keep track of. It works in the context of the story, but there's just no moment to rest, and that becomes a problem after the rest of the book has been so deliberately paced. I think that, by limiting the timeline to one year, it cheapens the value and difficulty of everything that the kids had to do. This was supposed to take them years, to be incredibly difficult, and when they solve the mystery in a year, you just get the feeling that it wasn't really that difficult to work out. Would have been much easier if Dumbledore hadn't been such an uncommunicative ass.
Luckily, it's only a problem I felt until I was done reading. As you're reading that last fourth of the book is exhilarating, surprising and shocking. Rowling brings out all the big guns, taking things into unexpected, darker territory, and it's a thrill to read. There are moments where the writing it just beautiful--you feel that you're right there on that crazy journey with Harry, and it's a testament to the characters Rowling has created that you feel incredibly deeply for them when they're faced with their final choices. It's beautifully done.
...Until you get to the epilogue. I don't even want to get that into it, because it'll just lead to another long, angry rant (Scorpius? REALLY?). Let's just say that the book ends too abruptly, and the epilogue is far too cutesy and clumsy to follow such an epic ending. There are so many questions unanswered, so many reunions we needed to see but never happened, that we needed so we could feel like the adventure was over for now. It's just terribly unsatisfying. I get the feeling that maybe Rowling was forced into writing a happy epilogue, and so it just feels tacked on and forced. It's too bad, really, because the rest of the book is a great read, and nice, concise ending to Harry's story. It came very close to being perfect, and I was left wanting a little more.