I personally rank book 7 as about equal to book 5, both of which are miles above book 6. HBP felt like a terrible soap opera in book form to me. Writing romance isn't JKR's strength, imo, and Harry seeming to focus so much of his attention on relationships right after losing Sirius and learning the prophecy seemed wildly ooc.
I found the wandlore in book 7 interesting, and Voldemort ultimately losing to it was in character for him (seeing as he had shown a habit of underestimating more subtle magics like Lily Potter's sacrifice in the past.) While I wished that Harry could have been shown to have expanded his duelling skills further (I would have loved a scene where he matched or even out-duelled Snape,) I think that the way that Harry overcame Voldemort through more a result of his choices, rather than his abilities, reflected one of the greatest themes of the series (at least imo,) that virtue is far more important than power.