Finally finished HBP and was not particularly impressed. The worst part about it was the way Snape was portrayed a whiney, childish, Anakin Skywalker-type bad guy. If Snape's supposed to be evil (for real or as a double agent) then make him believably evil. Even at the end when Malfoy couldn't kill Dumbledore he still came off as evil-er than Snape.
My problem with the previous books were mostly that I didn't find them in the least bit engaging -- and occasionally I found them unoriginal. HBP was replete with bits ripped off from LOTR, particularly at the end. First, Dumbledore has to do a spell to open the door to the cave, which is very similar to Gandalf's "speak, friend" door opening. And the cave behind it was similar. The monster in the lake was inside in HBP, outside in LOTR. Though the monsters in HBP were dead bodies, in LOTR the dead bodies in the water were in the death marshes. Oh, and the way they found the rope and the boat was like the end of Indiana Jones & the Holy Grail where they have to cross an invisible bridge.
Book 6 is more of a set-up for Book 7 than a true stand alone story. But I'm not so sure where it implies things are headed. It sets up the likelihood that the next book will not be set in Hogwarts. I think that is a lousy idea. I'm not necessarily enamored of the school but it strikes me that by having Our Heroes drop out of school and not graduate, it essentially negates all of the previous books. The last thing I want to see is the school shut down and Our Heroes awarded honorary degrees and great jobs after killing Voldemort.
Unless there's some kind of huge plot twist in the next book ("Harry, I'm your father," said Snape) then I think it's going to be quite a letdown. Maybe it'll have cool spells and lots of action, but it will be mostly sound and fury signifying nothing.