Firstly and foremostly, there is a HUGE difference between writing a novel and writing a movie. Everyone loves to beat Melissa down, but the reality is, EVERYTHING she has altered or changed was approved upon by Stephenie as well as Summit. A novel, by default, makes a bad movie, and it isn't designed for movies... Visa Versa. I have yet to see a novel completely translated to the screen without changes, because they can't. Lord of the Rings, as good as the book is, was altered quite a bit for the film. The movies were really good, because Peter Jackson and his wife new what needed to be changed to make the story work for the screen. While purests will cry fowl, the over all end package was great.
In many ways, Melissa restrained herself for the sake of fans. Remember, Summit wasn't the first studio to make Stephenie an offer. They probably would have paid a lot more, and spent a LOT more on the movie, than Summit did, BUT they also wanted to take full control of the story and rewrite it. It might have created a better movie, such as was done for Jurassic Park, of which was one of the highest grossing movies of that time, but fans would have been upset.
So Melissa is walking a fine line. She's trying to adapt the movies the best she can for the big screen. IF she had written the fight scenes to show just how easily all the Cullens and wolves could have defeated Victoria's army, there would have been absolutely NO drama. If the audiance doesn't feel the drama, I don't care how freaky and scared Bella looks, it ain't going to work. Sorry folks, that's how this biz works.
As for missing scenes that I wish they would have put in...
I would have liked them to rework the scene where Bella reclines on Jacob's wolfy back. They sort of incorporated it somewhat into the final product, but I thought her laying across his back would have been a bit more tender. I also thought it was strange that they didn't include Jacob running away in wolf form at the end. I take it, they don't plan on him running away then... It makes me wonder, if they plan to ignore his thoughts completely and just keep BD in Bella's perspective. hmmm...

