As I recall from reading them years ago, it was book 5 that I thought was....not tedious, but kinda...sprawling. It seemed to need some serious tightening up and could've used an editor to remove like 100 pages worth, imo. I don't recall thinking that about book 4. But b5 did contain probably my favorite scene of the entire series, the showdown between Dumbledore and Voldemort. That scene was extremely illuminating on several levels, both from characterization and motivation standpoints.
It was also the first major divergence in how well I thought the films adapted the source material. In the movies, it comes off like Dumbledore was just hanging on in the face of at-least equal power, if not superior, and possibly just barely hanging on. It didn't come off like that at all in the book. It had much more of a feel that Dumbledore was very calmly countering every attack and was rather confident in the battle, which posed the question "Why doesn't he just finish it, then?" The answer to which I think becomes more obvious in b6. The movie scene served to build up the terror of the villain, I suppose. But the book scene served to illustrate the very different worldviews the two had, and how they lead to the choices each made over the years.
I concur b7 was a strong finish, though I considered the entire series very strong overall. One of the most enjoyable series I've ever read, and with quite a lot of intricacy that demonstrates a very well-thought-out story from start to stop on the author's part. The ending highlighted another discrepancy with the movies, though in the final battle's case, I don't fault the movie for changing things up. I think the movie did what works for a movie there. If it had tried to mimic the book completely, it would probably fall flat, because it only works with the ton of exposition you're afforded in the book. And also, movies kinda need the high-octane action finale. There was just too much interwoven into the grand story that culminated in the ending she wrote to get across in a movie. So it diverted to another course entirely, in a way, which was just to have the grand battle royale between Harry and his foe. It seems to me--though not explicitly stated--that in the book, the way everything was set up, by the time the final battle begins, Harry has won already because of the sacrificial planning of many before him. Effectively, Voldemort is defeated before he ever gets the chance to duel. In the movie, it's more of a classic "You vs. me, buddy. Let's go." Which works well for a movie, I think.
I haven't re-read them, but I wouldn't mind another pass one day. Her writing style was so enjoyable that even if I remember the major plot points, half the fun of reading those is all the minutia, which she writes extremely well. Like you, it'd be interesting to see if and where my opinion changed over time.
