Personally I dislike making movies from Books except in the case of the Godfather and Shawshank Redemption. even Gone With the Wind paled in comparison to the book, though Rhett Butler could...
I love the JD Robb series and no actor could ever live up to my image of Roarke or Eve.
One of the worst series in book and movies had to be the Twilight series. The actors certainly couldn't act and the TEAM Edward and Team Jacob thing were really stupid. All the books were written before the movies even came out, so the audience knew there was never a chance of Jacob winning.
Though I liked the Harry Potter books and the choices for actors were ok, I didn't care for the directors perogative on what to show. The movies didn't do a good job at explaining the background enough.