The book was terrific, but it was not perfect, and here are five reasons why. I have to stress that overall I thought the book was a fantastic and worthy end to the saga, and it was more difficult for me to come up with 5 negative points than it was to come up with 10 positive points as I did last week.
I'm going to be spoiling the book again here, so turn back now if you haven't yet read it.
5. Wandering aimlessly
In a draft of the script for The Empire Strikes Back, one of the characters aboard the Millennium Falcon had a line saying "This is boring". This line was removed, because when the characters start to believe that their adventure lacks excitement, the audience will believe the same. Though its necessary in Deathly Hallows to have periods of idle time in order to stretch the book's timeline to one whole year, it doesn't inspire confidence to make the lack of activity and direction a significant plot point. When Ron and Hermione express disappointment on Harry's lack of direction in their quest, the reader starts to have similar doubts with the direction of the story.
4. Action scenes
I hate to admit it but Rowling isn't sufficiently good at writing coherent action sequences. I'm sure I'm not the only person that had a "Wait.. what the hell just happened?!" moment when Nagini popped out of Bathilda Bagshot. While nothing in Deathly Hallows approaches the chaos and confusion of the battle in the Department of Mysteries in Order of the Phoenix (the chapter where Sirius dies), there's a lot of action scenes in this book and a lot of opportunities to be bewildered with everything that's going on.
3. Sudden death
The death toll rises alarmingly in this book, with at least a dozen named characters wiped out with sudden, almost casual swipes. That's the way it is with war: Deaths are horrible, pointless, and plentiful. There's a death of a previously unknown teacher in the first chapter, and our beloved Hedwig dies in the fourth chapter (presumably to send a message of imminent danger-- if Hedwig can die, anyone could be next!). But there's no way to hide disappointment with the way that Lupin and Tonks were wiped out. "Oh look, there's the bodies of Lupin and Tonks. They're dead. Well, carry on...". Lupin was way too major and cool for such a forgettable throwaway death.
2. Deus ex machina
I didn't realize this one until it was pointed out to me, but the plot relies way too much on deus ex machina-- improbable plot devices introduced suddenly to resolve a situation. Wasn't it just a bit too convenient that Dobby appeared in Malfoy Manor at the exact situation where Harry needed a house elf to save him? And the Deluminator being a device to bring Ron back to Harry and Hermione, that was pulled out of nowhere. Even the Deathly Hallows themselves, the pillar holding together the second half of the book and the key to Voldemort's defeat, were never mentioned or hinted at before. If you look at it that way, the whole plot starts to look shaky.
Almost everyone I've talked to has something to say about the epilogue. Rowling mentioned years ago that she had written the final chapter of the epic tale of Harry Potter long in advance, and it shows. The transition from basking in the euphoria of Voldemort's death to the relatively routine banalities of "Nineteen Years Later" was way too sudden and jarring, and the effect had the epilogue just looking cheesy, even mundane. There should have been a Chapter 37 where everyone could finally come together in peacetime to mourn the dead and toast their success and generally to just cool down. Instead we suddenly have middle aged Harry and friends seeing their kids off at King's Cross station, living the pedestrian lives that normal wizards presumably lead. It certainly is a convenient way to end speculation of a "Return of Voldemort", but the end effect is disconcerting, and that is not the ideal emotion to have at the closing of such a grand and epic saga.