Books vs Movie

How many books have been translated well to the screen? How many, if any, surpass the book? I love books. They force me to use my imagination. When an author describes a character I get a picture in my head of what that character looks like and how they dress and act. Rarely does the description make it to the screen. However that doesn't mean that all movies from books are bad. Some adaptations have stayed fairly true to the authors intent. Then you have those that take the book and vomit out something using the characters names and perhaps some of the situations from the book but that’s about as close to the book as they get and put a disclaimer saying based upon the book by so & so. Right or wrong it just is. Sometimes they actually put out something fairly entertaining. My question is should directors and screen writers be forced to stay as close to the original as possible?