Books vs. Movies

I know, I know, it's the great debate, generally leaning towards books (of course!) But having recently read Neil Gaiman's graphic novel Stardust (after having seen the film), I was really surprised how THIS:



Turned into THIS:



I didn't really know what to expect going into either the film or the novel, despite having attended a Neil Gaiman/Charles Vess (the illustrator) Q&A Sneak Preview of the film last summer. Gaiman has a very C.S. Lewis type of narrative in the book, where he mentions that the characters

It interests me, then, why some movie adaptations are so freely changed and turn out well, whereas in other cases even the slightest deviation from the books can ruin a film version. What is it, I wonder that makes it allowable in some cases and not in others? Is it wholly a personal preference thing?

Already I've been wincing at the harder, more action-packed film version of Stephanie Meyer's smash-hit novel Twilight—but I seem to be the only one. From what I've seen of Neil Gaiman's fans are (though admittedly smaller in number) just as obsessive as say, JK Rowling fans, but I've seen no negative backlash about the film version of Stardust, whereas others cause uproars over minor changes? And I'm not talking about Harry Potter... that and the seven-book story arc is understandable. But I'm sure you can all think of a film you were tempted to walk out on for wreaking havoc on one of your favorite books. So what is it that makes the difference? Any ideas?

And on that note, just for a laugh, 30 Things That Should Never be Adapted to Film. I think my favorite is The Legend of Sisyphus, starring Christian Bale... Or possibly Sleep Hard. Ah, yes...