Back in June of 2009, I predicted that the changes from book to film will include:
1) Taking out the good humor of the original in order to make it “darker”.
2) Nevertheless being fine with inserting plenty of lame Jar-Jar/Gimli-the-Robot “comic relief”.
3) Gandalf, Bilbo, and the dwarves will all rely on their awesome kewl powers instead of wit, speed, secrecy, morality, and more wit. Expect lots of battles.
4) In the book, Fili and Kili are the only Dwarves who aren’t white-beards (old). In the movie, I expect they will all be young. Some will be female, and all different skin colors will be represented. (Sexual orientation, too, but that will be “left open to interpretation”.)
5) A few obligatory love-interests will be added.
6) Bilbo will be a skinny teen heartthrob type instead of a fat hobbit in his fifties who is fond of tea and handkerchiefs.
7) The Trolls, the Eagles, and the Spiders won’t talk but the Wargs will.
8) Not only the Gandalf-in-Dol Guldur subplot, but also many other made-up Lord of the Rings tie-in plot elements will make it into the movies and take up 25-50% of the screentime.
So far, mad-scary-accurate. Except for the lack of female dwarves. That we know of.