Something I found interesting about Eclipse the movie was the amount of material they used that was found only in BT. My sister, who hasn't read BT yet, was constantly asking me little questions.
For one thing, I was surprised in the amount of back-story and screen time they gave to Riley in the movie. All-in-all, he's one of those characters we don't learn a lot about in Eclipse and who dies during it's conclusion, so I never gave a lot of thought to him before Bree Tanner came out. But because Riley is depicted as the leader of the newborns in BT, while Victoria only a shadow leader, there was a lot more emphasis on him. I think it really added to the mystery for the movie that they focused on Riley and his apparent newborns; Who is this Riley? Why is he creating an army of vampires? What is his connection to the Cullens? By playing up Riley's role it throws off people who'd never read the books and didn't know of Victoria's involvement. So, thumbs up for that.
The Volturi. I LOVE the scene they added in where we seen Jane in charge of the group sent to investigate the Seattle newborns. It's something we wouldn't have known without BT, but this is the first time we see the true colors of the Volturi as they do despicable things while hiding under the false image of protecting vampire society. I thought they would do the scene where Jane and the gang meets up with Vicky herself, but the director really wanted the audience to be kept in the dark about her involvement with the newborns, so they had to go a different path to show this vital information about the Volturi - and they did a wonderful job with it. Again, another thumbs up.
And now a not-so thumbs up. Random camera panning to Bree Tanner herself with no explanation. Yes, we kind of understood who she was because of BT and her importance in the movie comes out later, but were the random shots really necessary? Only in one of the early shots of Bree did her appearance have any importance and that was when Riley was mumbling about her needing to stay alive because he "needed numbers". So they gave no back-story for Bree (heck, they didn't even give her name until the end) those close-ups of her face among the other newborns would just confuse people who didn't read BT; as far as they know, her only scene from Eclipse is her death.
I really liked that they added in things from BT, but some of them might no go over so well. There were a lot of things you wouldn't get unless you read BT, but because it's still a fairly new novella, the timing wasn't too great for the wide selection of fans. I know a ton of people who are only just now picking up the book, so the BT references went right over their heads. :/