I can't believe no-one has posted yet!
I think HBP is my favorite book so far (I haven't done the re-read for DH, and probably won't until after I have seen the HBP movie). JKR did an awesome job with mixing the seriousness of the situation (LV being back, Harry's learning what he has to do, Dumbledore's death, Snape's alleged betrayal) with wonderful humor and wit. I often found myself laughing out loud at some of the humor.
I don't really have any predictions of what will be in the movie or left out of the movie or changed so much that it doesn't resemble any part of the book. I have seen plenty of trailers to think I'll be pleased with how this movie relates to the book, but I have tried NOT to watch all the trailers since I want to enjoy the movie without anticipating every little scene.