Will you kill me if I said the best part of the movie was the twist even though it wasn't in the book? It was the only part of the movie to get a reaction out of me. I get the reasoning behind the twist, but a part of me feels like they only added it because they needed to make the movie 2 hours long. If they had kept to the book and maybe not split it up, they wouldn't have needed the twist no matter how shocking it was.
Leaving the twist out, here's my famous list of differences:
1) Jasper's ability: Edward & Alice weren't the only ones with an ability, Jasper's ability is to alter one's mood especially in newborn vampires, which becomes a huge asset to Bella whenever her emotions got the best of her.
2) Reneesme's biting: part of being half vampire/half human is the fact that Reneesme likes blood along side human food and as a knack for biting people especially Jacob. This becomes important when Nahuel explains that only the males bites are venomous.
3) The Quileute are shapeshifters not werewolves: One reasoning Caius comes up with for killing the Cullen's is that they associate themselves with werewolves. It is then explained that they are not the Children of the Moon, they they are shapeshifters who identify themselves as wolves.
There are a few more differences, but I do have to say that they stayed true to the storyline as closely as they could. I still think it could have all been one movie.