I read the book by Phillipa Gregory and became entranced by this period of history, subsequently reading several history books on Henry VIII and his wives. The book took some creative licenses, but was still riveting, and for the most part, historically accurate. The movie, on the other hand, avoided delving into most of what made this period in English history so fascinating - namely the religious and policial implications of Henry's obsession with Anne. The movie made it seem like these events occurred rapidly, when in reality, Mary Boleyn was with King Henry for several years before he lost interest (and bore 2 children by him, not one), and Anne struggled to maintain Henry's interest for over six years before becoming Queen.
Natalie Portman does an excellent job in the role of Anne Boleyn, but I think this movie would be confusing for anyone not familiar with the history.
Generally, movies based on actual events that veer off-course from the "truth" annoy me. They leave an inaccurate impression on the viewer and do injustice to history. However, the film was still entertaining and would be worth a rental.