What I loved about book 6: Snape was in it right from the start. Snape was D A D A professor; Snape was in the story a whole lot more; and Cho Chang was in it a whole lot less. And Harry and Ginny finally gotten over themselves and admitted to their feelings for each other... sorry but I see them together more than Hermione and Ron. Even after Snape did what he did Hermione's still on his side... you go girl!
What I hated about book 6: Hermione suddenly turned from clever, brainy know it all to someone a bit petulant and whiny... she just didn't fit with the Hermione in the first five books; Snape killed Dumbledore... I am one of those that live in hope. No Lucius Malfoy... *grumbles and groans*! More Lupin... sorry not a fan of the Werewolf; or his pet dog and Stag.
Overall I prefer Order of the Phoenix to Half-Blood Prince; but the way it's been going I am probably going to love Deathly Hallows a lot more than HBP... Especially as we're going to get the answers to several unanswered questions.