Well, I've finished reading the book. Overall it's not bad, about what we've come to expect from Ms. Rowling. There are some flaws, however, which I will try to discuss without spoiling the story for those of you who haven't finished yet. There are, however, spoilers from book 6 here.
First, as I mentioned in my previous post, book 6 ends with the bad guys cleaning up with Harry because he's unable to make spells silently. This, I thought, proved that Harry was, compared to his elders, completely unprepared to deal with adult wizards who were performing magic. Ms. Rowling didn't address this at all in the 7th book and instead most spells were spoken aloud and it was considered a good defence to render your opponent mute. This brings us closer to the other books where such things were normal, and highlights the problems with book 6.
Secondly, there are things that happened in book 7 that seemed a little incredible. As you can probably guess, there is a war going on between the bad guys (Death Eaters) and good guys (various). Naturally the Death Eaters are making headway and a decisive victory is required by the good guys but this victory is elusive. Things have to get worse before they get better, otherwise it's a boring story. The problem is that things get worse so fast in book 7 that it's really not believable that the wizards would let it happen. People achieve positions of power without the outcry you'd expect from others. I'd expect to see, or at least hear about, good guys resorting to more extreme measures in order to prevent the ascent of evil: We are, after all, talking about bad guys so EVIL that nothing is beneath them. I mean, they have spent the last several books trying to kill children, among other nefarious deeds.
Finally, the book contains some rather predictable plot "twists" which many people have seen coming. Thankfully most of these were reasonably well explained but still it would have been nice to have a bit of surprise. The only part that surprised me was when one of the characters said the word "Bitch".
The book does have its good points, but the main improvement over the previous books is the acceptance by the characters that they are at war, and that lives are truly at stake. One person says "we duel to kill" and this is indicative of the tone. However there are still too few good guys using Avada Kedavra. Overall, the book is a pretty good end to the series.