Do the follow perfeclty? Of course not. But unfortunately I've come to learn when it comes to book to movie adaptations it will never be perfect, not even close. Things will have to be changed, rearranged, or even left out. Especially considering each book is over 500 pages. (EC is over 600!) It's hard to condense that much material into 1 2 hour movie. (That's partially why I'm glad BD will be 2 movies.) There are some things I really wish they had kept in the movie from each book. Make each movie just 20 more minutes & I think they'd be able to make most fans happier. And I think each movie has gotten better when it comes to getting the book across. And it does kind of bug me that the movie version of each character comes across different. For exampe in EC Jacob is tolerabl while in the book to quote Bella he has his moments where he bugs the hell out of me. I honestly wonder sometimes if Melissa Rosenberg is Team Jacob. Anyway. The books are always better but for the most part I do love the movies.
I think Twilight followed the book quite well, New Moon kind of did but Eclipse was kind of butchered. Mainly the best Alice scenes were cut out, I think the tantrum she has over the wedding would have been hilarious, not to mention the "This hostage stuff is fun!" part. They also cut out Edward's controlling behavior, he doesn't let Bella just take off with Jacob at the school, she has to sneak out to be with him. They left all that out and I think it was important to show that Edward (and Alice) was extremely controlling towards Bella.