I recently read The Caine Mutiny -- have you ever read a novel after seeing its stage/screen adaptations, and been surprised to realize that an apparently minor character was actually the hero of the book? It hadn't occurred to me that Willie Keith, played by the fifth-billed Robert Francis in the movie and not much of a presence in the play, is the main character of the book. It's not the only time when an important character from the novel, or even the hero, is less important when the story is adapted to a different medium; for some reason it seems more striking than usual because the most important part of any adaptation is the court-martial -- that's the part that is the basis for the play, after all -- and the book's "hero" isn't a very important figure in the court-martial scenes.
Actually I found that the biggest weakness of the novel was the fact that it was about Willie, who is an asshole. And while it would be one thing if Wouk had actually set out to write about an asshole, he appears to think he's writing the story of a callow youth who becomes a man due to the experience of war. (Wouk signals throughout the book that he's trying to write an alternative to the war novels written by the likes of Tom Keefer, about how bad war is and how rotten the military is; the point of Caine is that while war is awful and you have to put up with horrible commanders, the experience can also make people better and stronger.) But that's not what Willie is. He starts the novel as a snobbish mama's boy who gets everything wrong, and he continues to be that way through most of the book. It doesn't help that Wouk's sexism sort of wrecks the romance plot of the book. Specifically, when Willie feels contempt for May because she slept with him (the slut!), Wouk seems to treat this as if it might possibly have some validity when in fact it just establishes Willie as a despicable schmuck.
Still, a novel with a weak hero can still be worth reading -- if an uninteresting or unsympathetic hero destroyed a novel, many of Dickens' novels would be worthless -- and the good parts of Caine deserve their iconic status. The steel bearings bit in particular, I don't think any adaptation has really added much to it; it works better when you can imagine it, and the famous Barney Greenwald speech, preachy though it always is, is one of those things that works better on the page when an actor is not making a meal of it.
Also, while Wouk's conservative viewpoint sinks him when it comes to female characters (in this book at least) it does help a lot in giving an entertaining slap in the face to the pop-Freudianism that had infested American novels, plays and movies since the '40s. Actually in some ways it's more interesting for its viewpoint on literature than its viewpoint on war or the military. Tom Keefer is a typical American literary intellectual and, like most literary intellectuals of his period, he analyzes everything in terms of pseudo-Freudian nonsense. His fake-Freud "reading" of Captain Queeg takes in Steve Maryk -- who figures that if Keefer is a brilliant intellectual he's got to be on to something. The theme of the novel is, to hell with Freudianism, stop complicating everything: sometimes people are just mean and nasty and stupid and there doesn't have to be a deep psychological motivation for it.