Naturally for pure bibliophiles Movies are no substitute. For the rest of us the movie is the closest representation to the story we will see and we can compare and contrast to the story as it is written.
Regardless of which side of the fence you may be on the movies is the only representation for many. And having them in one collection adds an esthetic plus. This is what movies are all about.
Even if you already own one or two of the films it is worth re-purchasing.
You can read the individual reviews for each film to get a feel for what this series of films is about. Notice that they changed directors on the third film and the feel of the series. You can speculate on the next film; however I would buy the set now and make a decision in the future as to a set of four movies.