And the verdict is...
So either Severus Snape is a triple- or quadruple-agent who killed Dumbledore because such a sacrifice was necessary for the ultimate downfall of Voldemort, or Severus Snape is a painfully two dimensional character of evil who managed to hoodwink the wisest wizard of the era.
One of these possibilities would indicate that J. K. Rowling is a genius and has surpassed her own talent for writing unpredictable plot-twists. The other would imply that she peaked in her ability to write morally complicated and believable characters in the 3rd, 4th and 5th books, and is now hurriedly resolving the loose ends of the story by turning the least likeable character into (gasp) an actual villain.
I'd like to believe the first option, but having been burnt by the messily concluded X-files, Star Wars prequels and Matrix trilogy, I'm unwilling to get my hopes up.
Other things I didn't like about the book:
-The conversation between Snape, Narcissa and Bellatrix just didn't flow very well. It didn't sound like three people in their forties who had an intensely complicated history serving the same Dark Lord. Snape was too loquacious, Bellatrix sounded whiny. I enjoyed the fleshed out Narcissa though.
-No follow-up on the accidents in the Ministry in the last book. Ron was attacked by flying tentacled brains, for morgan's sake. Shouldn't that have more lasting effects than some welts on his arms? What was the significance of the veil that Sirius fell through? What about the room that wouldnt open for them? Will any of this be resolved in the last book.
-Still no sympathetic Slytherins. There are hints that Draco is more interesting than previously indicated, and the new Potions dude is entertaining, though smarmy. But are all Slytherins (and hence a quarter of the British wizard population) as self-serving and stuck-up as the ones we've seen?
Things I DID like:
-Voldemort's personal history! Did anyone think Oliver Twist when reading about the poor pregnant mother with nothing to her name but a locket that got pawned? And the downfall of Slytherin's lineage was believable - a family so proud of its heritage that it refused to "dilute" its blood by marrying outside the family, and so reckless and ostentatious that it squandered its fortune. Interesting, though, that Tom M. Riddle was a bullying, manipulative git before even darkening Hogwarts' door step. I compare this with the only HP fanfic I have thoroughly enjoyed, The Broken Victory, which tracks Riddle's transformation from an ill-treated but morally incorrupt orphan (like Harry) into a smooth, manipulative murderer.
-The humor. "No need to call me sir", Won-Won, the banter between hermione and ron.
-Harry's report card. It's nice to see a report card that isn't mine, for a change :)
-Lots of other stuff.
On the whole, I like it better than CoS and less than OoTP, perhaps comparably to GoF.