Biggest surprise: Natalie Portman as Anne. I was a little upset when I saw that she had been cast. She's Queen Amidala, she's Novalee in "Where the Heart Is", she's sweetness and light and sunshine. I just really didn't think she could pull off Gregory's smoldering, witty, ego-maniacal, and even kinda bitchy characterization of Anne. I was wrong, wrong, wrong. I only wish they had made time in the movie for some of the sexually charged banter that goes on between Henry and Anne in Gregory's book.
Biggest whitewashing of historical fact: At the end of the movie, Henry really believes Anne had sex with her brother George. In real life, not so much. The real story is that after Anne's second or third miscarriage, Henry was ready to be rid of her so he could marry wife number three, Jane Seymour. Anne was charged with having adulterous affairs with five men, one of which was her brother. The charges are generally thought to have been trumped up, with Anne and the men in question in completely different palaces on some of the dates in question. Allegedly some of the men were even offered pardons if they would just confess and implicate Anne. None did except for Anne's musician, Mark Smeaton, who was tortured into confession because he was a commoner.
Biggest reduction of depth of character from book to movie: George Boleyn and William Stafford. In the book George is portrayed as kind of a jaded playboy. He does the court-thing because that's what he has to do, but gradually gets more and more disgusted with himself as the book goes on. William Stafford--the guy Mary eventually ends up with--on the other hand is kind of a foil for George in the book. Stafford is the good, salt-of-the-earth guy who recognizes life at court for the nonsense it is, and ultimately takes Mary away to the good life she loves in the country. I was kind of sad that they didn't choose to develop all of that more in the movie.
Biggest change from book to movie: This is one I actually didn't mind. In the book it is at least strongly indicated that George and Anne had sex and had a deformed baby as a result. In the movie they almost have sex (in order to save Anne's life by giving her a baby) but stop short. I think if you read more of Gregory's books (in particular "The Virgin's Lover") you can see that she tends to think the very worst of both Anne and Elizabeth (and conversely tends to adore both Katherine of Aragon and her daughter Mary--see "The Constant Princess"). I'll admit it's a bias that I don't particularly appreciate. The historical facts don't specifically prove her wrong as to Anne (Elizabeth is, in my opinion, another story), but I think she pushes them just a little too far. So, I was glad that Anne and George remained just brother and sister.
I'm interested to hear what everyone else thought, so comment away if you've seen it!