My favorite adaptation isn't really an adaptation at all.
I refer, of course, to The Princess Bride. Author William Goldman claims to be abridging a classic tome by one S. Morgenstern of Florin, and through Goldman's little notes about what he's cut, what he's kept, and why, we get the feeling we're enjoying a favorite tale along with him. But florin is nothing but currency, no one named S. Morgenstern ever lived there, and without Goldman, no part of The Princess Bride would exist. It's not hard to see who gets the credit there.
In other cases, though, the point of an adaptation can be harder to find. I've heard many objections to the abridgements of classics for early readers. Personally, I don't object to their existence; if a six-year-old is interested in a sneak peek at what this Oliver Twist business is about, more power to him or her. I just hope parents and other gift-givers aren't motivated by a desire to be able to say that the child in question is reading "classics." After all, there are plenty of classics whose originals--with their original voices intact--are intended for new readers, and I'd hate for those readers to miss the real Frog and Toad or The Hundred Dresses because they were limited to a not-quite-real Secret Garden or Moby-Dick.
But there are adaptations that are works of art in themselves. Some of the graphic novel versions of existing works are somewhat perfunctory; others may be helpful in understanding those works, but are otherwise forgettable. But then there are Gareth Hinds' graphic novel adaptations. Just look at The Odyssey. I think I've made a few maybe-graphic-novels-aren't-junk converts just by holding it up.
And then there's The Flint Heart, Katherine and John Paterson's "freely abridged" adaptation of Eden Phillpott's 1910 novel. I've read only a brief excerpt of the original work, but my impression is that the Patersons did something really smart: they preserved the voice. It's not dumbed down, and the funny lines keep on coming. It's easy to preserve plot in a retelling (though many film directors could stand a lesson in that). But the new Flint Heart also holds onto other important elements that make a story worth reading. If this edition brings a near-forgotten story to more readers, I think it serves a worthwhile purpose.