If you read Jane Austen, you know that Northanger Abbey is the runt of the litter. It's the scrawniest -both physically and in terms of plot- and it's the sorriest, being mostly a joyless exercise in parody. Gothic novels were popular in Austen's day, and Northanger Abbey's heroine is a devotee.
Because I disliked the book, it was with trepidation that I approached the movie. Masterpiece Theater adapted Northanger in 2007, and last Friday I finally broke down and watched. And was, to my shock, diverted! Northanger The Movie took what had been a limp, somewhat mean-spirited satire, and turned it into a tongue-in-cheek confection. Perhaps because the hero and heroine were played by actors who embodied, as opposed to scorned, their characters' feelings, Austen's novel was injected with much-needed humanity while losing none of its fun.
It's very rare that a movie tops its book. I can't think, off the top of my head, of any other examples. A friend from childhood suggested that the film version of Atonement was better than the novel upon which it was based, but I'm unable to judge for myself: the novel ravaged -and ravished- me so thoroughly that I'm unwilling to stomach a second helping of the plot.
Hayao Miyazake's surreal riff on the Diana Wynne Jones novel Howl's Moving Castle is luminous, but so far removed from its source material that comparison is pointless. And two film-novel pairs that come to mind -Little Children and The Hours- enthrall equally in both mediums.
Maybe Blade Runner: I didn't much like Dick's short story. Any other nominations? It's an interesting category...