I don’t think that will ever happen, really. With novels, the writers are free to explore their writing space, while you have to place certain restrictions in a movie script, despite H-wood’s current devotion to best-selling novels (a result of their assumption that if the book sells, the movie based on it would definitely be a hit, too).
For example:
In a novel, when two or more characters make interactions with each other, the writer could just describe their thoughts and feelings at that time. In a film, however, the actors/actresses have to show us their miseries and joy, not tell us. In fact, Angels & Demons is probably one of the biggest victims of this factor.
Hence, a script has to be changed. You can’t just have Spider-Man telling us how emo he felt upon his uncle’s death for the whole hour and a half. Speaking of which, there’s also the other factor, the time constrain.
Nowadays, with Hollywood playing so safe that they give almost a hundred percent support to the cast working on a novel-based film, the film makers have more space to create a longer movie, so time is not a real problem. However, there’s always that certain sympathetic guy at the corner who was mocked, judged, and unfairly criticized.
Watchmen is one example. It would had been better to make it into a whole TV series rather than a film that had every aspect of the graphic novel crammed in a one hour and a half movie. Once you try and force everything in, the movie’s quality is, even more so than those given freedom and space, diminished in the confusion and chaos.
So, when will a movie be as good as the source novel? It’s a rare occurrence, but under the right team and a skilled director, such miraculous sights do appear, and they would probably not be one with a big title like Lord of the Rings (which seemed to have disappoint some fans of the novel). And that was directed by PETER JACKSON. If he can’t perform such miraculous act, I doubt anyone could.
Maybe Cameron. <_<"