I have read all of the books twice over, and am in love with the story line of the twilight saga. Eclipse was a little weird for me. As a fan of the books, I always feel like they should put in all of those little details, because the movie will be as much as we expect, and although it might be long, for those people who haven't read the books, things will make so much more since. I feel like there was so much left out, about Bella and Jacobs back and forth friendship/relationship, the history of the tribe, the amount of time Bella spent with Jacob and Alice, so much that you just don't see in this movie. It mostly focused on the "love triangle" between Bella Jacob and Edward. It was pretty slow moving and the climax of the movie was there and gone before you even realize it. It deemphisized the battle so much that it barely stood out as the major focus of the movie, which it was a major focus in the book. I still loved the movie, and will always want to see more of them, I just think if they waited a few more months instead of rushing to put the next movie out, they could have put more attention to detail. Also, Bryce Dallas Howard just didn't cut it for me. I don't see why they replaced the old Victoria, because she fit the character so much better than Bryce does.
If you love the first two, I wouldn't hold back on seeing it, because you will want to keep up with the story and it was good. Just be prepared that it will be more slow moving and romantic, and not nearly as action packed and exciting as the previews have made it out to be.