In a sign of how the word "classic" is indiscriminately applied to any movie more than 20 years old, Variety's report on Mike Myers' upcoming remake of The Secret Life of Walter Mitty refers to "The Danny Kaye Comedy Classic." Kaye's Secret Life of Walter Mitty is no kind of classic; as a movie, it's no better than okay (like most of his Goldwyn movies, it's too polite and plush to make good use of his talents), and as an adaptation of James Thurber's story, of course, it's a travesty. (Though in fairness to the adaptors, a "faithful" adaptation of the original story would last about twenty minutes; they had to come up with a new plot in order to make it a feature.)
The article doesn't say what approach the new movie will take, or whether it will be closer to the original story. A problem with adapting "Walter Mitty" today is that the techniques Thurber used, which made the story unique at the time, are over-familiar today. Fantasy sequences were nothing new when Thurber wrote "Walter Mitty," but what was new was the elaborate way he connected the fantasies to the real world (having some real-life thing transition Mitty into his fantasy, and having something in the fantasy merge back with reality) and the connections between the various fantasies (like the running gag of having a sound described as "Pocketa-pocketa-pocketa" in each fantasy, coming from a different machine each time). It made the story a flowing, effortless whole instead of a series of unrelated sequences. This stuff was immediately influential; the 1945 Broadway play Dream Girl, by Elmer Rice, uses exactly the same techniques in moving from the real world to the heroine's fantasy world. And now they've been used so often that they no longer set "Walter Mitty" apart. Meaning that all you're left with, in adapting the story, is a wimpy guy who fantasizes about being a hero -- and that's not the most original premise; it never was.