Of all the books in the series so far, this is by far the one with the unhappiest, and least satisfying, ending. It seems to me that it is in fact the first half of a two-book arc rather than a closed tale in itself, which is not in any way uncommon in fantasy fiction, but took me slightly by surprise in this series because the other novels have been so self-contained.
Spoilers ahead for the two or three people on the planet who have not yet read the books/seen the films/absorbed the gist from the general cultural soup. The biggest surprise to me in this novel was the death of Dumbledore, not because I wasn't expecting it (if ever there were a sacrificial king-figure set up to be replaced by the younger, stronger king, it is he), but because I was expecting it in the last book, not here. I was therefore slightly stunned and spent the fairly lengthy denouement of the story vaguely hoping that there would be some magical resurrection. I rather admire Rowling for not falling into that temptation. Dumbledore is not Aslan, Christ or Gandalf, it seems.
That Snape is a double agent being set up for redemption in the last book seemed to me also reasonably clear as I was reading this volume. That being the case, it was necessary to give him some very pressing reason to commit the ultimate treason - the murder of his leader - and that reason was the preservation of the nasty child (but still a child) Draco Malfoy from the consequences of being forced into that same act. I would have been happier if we had seen Snape make his irremediable vow to Dumbledore himself, rather than to Draco's mother. However, introducing the "mother's protective love" element resonates with Harry's story, I suppose.
Unusually, I found the unfolding of this novel a bit clunky - the long flashbacks to Voldemort's past seemed very expository. Perhaps this is because I was not terribly interested in having Voldemort's character fleshed out, preferring to have him as a featureless monster. I know for a fact that my other complaint of tedium is entirely my own bias: I am simply not interested in angsty teenage romance, which drives much of the Harry, Hermione and Ron part of the plot. The obligatory new professor (this time a pompous social climber named Slugworth) wasn't terribly memorable, either - but at least he wasn't Dolores!
All that said, tedium here is a relative concept. I still found this novel a page-turner, and I liked the nice clear metaphysical problem laid out (the soul divided in seven, each part enclosed in an object to be destroyed, the last object being Voldemort himself). The fact that that particular task is not completed by the end of the novel was enough to drive me forward quickly into the last instalment.