The SHawshank Redemption, in my opinion, is one of the best adaptations in that it improves on the written material immensely. The only film I've seen do so in my memory is Curtis Hanson's LA cONFidential which takes a large overstuffed novel and pares it down into a simpler story while levaing the narrative intact. (Ellroy, for the record, says he hated the adaptation unlike King who was fine with Darabont's changes. Some authors are just like that.)

Long novels rarely adapt well to film whereas shorter ones tend to work better. John iRVING's novels frequently make better movies but the author has to doa lot of pruning. The Door in the Floor is an adaptation of the first half of Irving's A Widow for One Year. I eventually read Irving's book years after seeing the film and not only did I like the movie better I really thought Irving would have better off without the second half of the book. This may be my own issues: I tend to find much of Irving's work overrated. By contrast many of the best adaptations I've seen over the years have been adaptations of graphic novels, not just comic books but more serious works: Road to Perdition and History of Violence are among the most prominent that come to mind.