Up until films 7.1 and 7.2, I haven't really liked the films. They've changed too much or left detail out - one of the biggets mistakes IMO was saying that the Horcruxes could be anything, rather than that they had to be important. But these two films have rescued it for me, and most people on the forums should know how massive a fan I am of the books. Few people here will have read them more or know them better than me.
To all those complaining about the differences between book and film, you just have to accept it. Some things work in a book that just cannot work in a film. If you're interested in why I think they made the changes they did - and why they work for me - read on, and bare with me.
Take the way Voldemort dies in the book - there's a big fight, with Harry sneaking around under his Invisibility Cloak, then three pages of dialogue (call that about three minutes) then a tiny moment where Voldy's curse backfires. So, would that work in a film? You've just spent eight films building up to an action ending, and the hero and villain stand talking to one another before two seconds of flashing lights? No, it wouldn't work. So I'm happy with the way Voldy died - especially with the bit about Harry not being invisible, which I always thought was a tad cowardly.
About the Shrieking Shack being replaced by a boathouse. Firstly, there must be some sort of boathouse in the books, even if it's not mentioned explicitly (JKR does mention a 'harbour' beneath the castle in Stopne) as the first-years always arrive and depart the castle by boat. And IMO the reason they replaced the Shack with the boathouse is to both avoid the tunnel that leads to the shack (a scene of your heroes crawling to confront someone is a tad anticlimactic) and to have Voldy closer to the action - the Shack is almost twenty minutes' walk away. So I'm happy with that change.
Lack of centaurs and house-elf attack - centaurs are removed because the 'Harry's alive'! moment was moved away from the forest, so the centaurs would have to cross the bridge, which the couldn't do quietly, etc. House-elf attack...well, it's a bit cheesy on film to see a hundred foot-high pygmies stabbing at peoples' ankles with forks and the like, not to mention that it limits the camera angles you can use. Oh, and they never really mention the fact that there are loads of house-elves at Hogwarts in the films anyway - you only ever see Dobby and Kreacher. So I'm not too bothered about that.
Harry not fixing the Phoenix Wand with the Elder Wand - well, the P.W. was broken in 7.1, and isn't mentioned in 7.2. So that's one reason not to include it. Also, it detracts from the drama of him breaking the E.W. from a cinematic point of view, so that's another reason.
RE: Bridges. JKR never mentions any bridges - she explicitly mentions that the doors to the entrance hall open onto a smooth, sloping lawn. The bridges are included for a couple of reasons: firstly, it means that you can set Hogwarts atop a cliff, which is more dramatic. Secondly they added a second bridge because they wanted to blow one of the bridges up - but then no-one could get to the castle if there wasn't another bridge. IMO, not a problem, really.
As to the Battle of Hogwarts taking up almost this entire film, that's why they made two films - so that the long, pausing dialogue scenes were put into film 7.1 (with a few action scenes to keep the tempo up - Battle of Little Whinging, Shaftsbury Avenue [instead of Tottenham Court Road, for some reason], Godric's Hollow, Malfoy Manor) and the big battle becomes 7.2. In all fairness, battles work very differently in books than they do in films. If a book tried to describe exactly how a swordfight happened (X parried high but stumbled over some rubble, so Y kicked his other leg, which X just managed to get out the way in time, bringing down his sword as he did so...), it drags. You can't be that detailed in writing, so action sequences are always much shorter in a book than they will be in a film. The Battle of Hogwarts, including the Prince's Tale and King's Cross, takes up more than 100 pages. It took, I would guess, 50 minutes in the film. That seems to me to be about right.
The objects didn't burn them because they didn't need to. If you're being crushed beneath a tonne of metal, are you really going to care whether it's burning you or not?
Now, if I were to pick something that I thought most definitely didn't work in 7.2, it was Neville's inspirational (read: cheesy) speech near the end. I mean, apart from it being horribly cheesy and badly written, why on earth did Voldy let him say it?
