In my review of Harry Potter and the Deathly Hallows Part II, I said I would come back after the film opened and discuss how differences from the book were handled. Since the film is off and running to a spectular start, it seems okay to discuss "spoilers". Those who haven't seen the film yet, stop here. Then go see the film.
The only change with which I had much difficulty was utterly dropping the Dumbledore/Grindelwald backstory. My biggest complaint is that this was set up with some effort in Part I, then completely ignored in Part II. Was this about keeping things moving? Or avoiding the "Dumbledore was gay" controversy? Departing from the principle narrative for two flashback/explanation sequences would have been problematic for the film, and Snape's was more important. But leaving such a large plot thread dangling isn't very good storytelling.
RON AND HERMIONE'S KISS
I missed the ouse-elf revolt, but it clearly wan't going to happen in this movie, what with the way S.P.E.W. had been utterly left out of earlier films. I found the action sequence in the Chamber of Secrets to be thrilling, and, after dealing with Ron being a prat through so much of the previous film )I know, it was the influence of the ring . . . Um, Horcrux), I liked seeing him act decisively and with confidence in snogging Hermione. All things considered, I'm good with this one.
FRED'S DEATH/THE WEASLEYS
I have to admit, Fred Weasley's death didn't have quite the same impact in the film that it did in the book, mostly because it took place offscreen. However, the scene with Fred and George atop the Hogwarts castle, simple as it was, moved me quite a bit, and was, for me, a more satisfying farewell to the Weasley twins (probably my favorite characters) than the book gave us. Not seeing Percy's return to full Weasleyhood portrayed in its full glory was sad, but again, that was an opportunity they gave up three or four movies ago, and fat has to be trimmed in a movie. My feelings are certainly mixed on this one, but I accept the way it turned out without much consternation.
Overall, what matters most to me is that the filmmakers so utterly captured the spirit of the book, and made an excellent film. I admit I wish that Peter Jackson style extended editions of the films were on their way, restoring most of the missing elements from the books. But, even those extended editions of LOTR changed and cut quite a bit from the books (as much as I revere that series as one of the greatest in film history, I think there were more cuts and changes there that disappointed me than in the Potter films), and that's just unavoidable. I'm quite happy that, to get the full experience, one still needs to read the books.