From what I read, Prof Tolkien abandoned the rewrite of
The Hobbit because he realised that if he did it in the style of LOTR then the story wouldn't be "The Hobbit" any more but something else - the essence of what made that story special would have been lost.
As for the Hobbit 2 film version, thanks to the EE I know that...
--the first film ended with Barrels Out of Bound. the "cliffhanger" is Bard showing up and aiming an arrow at them. also there is no protracted Thrain vs. Azog fight when they're up in the pine trees.
--film 2 opens with them on Bard's boat not trusting who he is. There is no Dwarve vs. Smaug sequence in this version.
That's interesting to know. I wonder why they wouldn't have ended it with the Dwarfs being captured and locked up in the Wood Elves' prison though? It's a natural pause in the narrative, there's already been the climactic battle for the movie (the fight against the spiders) and there's the glimmer of hope for release in the form of invisible Bilbo. In addition, it's a good way for an unspecified amount of time to pass, in between the movies. The way it stands now (in DOS), mere days seem to pass in between leaving Beorn's house and the arrival of Laketown. But that's consistent with
Jackson's Geographical Scale, I guess
I'm probably in the minority on this, but I wish they kept Arwen in Helm's Deep. At least then she would have been contributing directly to the story and could have been part of the army. They had Elrond's sons with them in the book, so why not her? (not at Helm's Deep, I know, but later)
It would have been a controversial change but he had already substituted her for Glorfindel in FOTR so why not? In the end, sending a bunch of Elves to fight (and get slaughtered) was just as much a deviation from the book, not to mention making Elves look like very weak fighters. Plus ruining Arwen's character, as others have mentioned.
Maybe she would have been injured after the ride out (since Liv Tyler can be seen from the back in the film during that charge) and so she was rushed to Lorien for healing, which would then lead to her surprise appearance at the coronation (since Aragorn last saw her near death).
Having her injured in some grand heroic fashion would raise the stakes for Aragorn, since he would blame himself. Hell, Elrond can even turn up to collect her, dropping Anduril off in the process just like in ROTK if you like! Then Arwen can spend the next film dying, feeling sad etc before turning up to get married in the end.
Now, I know Jackson originally had them fighting side by side against the resurrected Sauron at the gates of Mordor and I'm glad he nixed that idea (plus her arc would then be duplicating Eowyn's). But since he made so many other additions to the story, why not throw the character a bone and do this too/instead?