I think there are two kinds of good adaptations when you come right down to it: those that take the source material apart and remake it into something different, and those that want you to experience the source material as exactly as possible.
Kenneth Branagh's Hamlet is one of the latter. Check out this exchange (and I'm picking one with R&G just because I love them and Rosencrantz and Guildenstern are Dead):
Nay, good my lord, this courtesy is not of the rightHAMLET
breed. If it shall please you to make me a
wholesome answer, I will do your mother's
commandment: if not, your pardon and my return
shall be the end of my business.
Make you a wholesome answer; my wit's diseased: but,ROSENCRANTZ
sir, such answer as I can make, you shall command;
or, rather, as you say, my mother: therefore no
more, but to the matter: my mother, you say,--
O wonderful son, that can so astonish a mother! ButAnd now look at the Kenneth Branagh version:
is there no sequel at the heels of this mother's
Kenneth Branagh's version of Hamlet is set 200 years in the future, and yet, there is no actual content changed. He uses the medium of film very effectively to emphasize funny or sad bits, and to keep the audience engaged with characters like Ophelia who might normally fade into the background, but all of the dialogue is exactly the same.
This is not a mark against his creativity. Kenneth Branagh wanted to bring Hamlet to life, and he did it wonderfully.
So, then there's the other way.
The Eagle is a (sadly) little-known 2009 Channing Tatum and Jamie Bell movie that was marketed as a historical action movie instead of the character study it really is. This isn't even one of these movies where you have to dig for the true meaning - nope, every single last bit of it is about the relationship between two men whose relationship changes from master/slave to brothers.
Look at this film clip, and then read the text of the book, of the same scene:
And in the book:
“Are you sure that you can trust that barbarian of yours in a venture of this kind?”
“Esca?” Marcus said in surprise. “Yes, quite sure.”
The other shrugged. “Doubtless you know best. Personally I should not care to let my life hang by so slender a thread as the loyalty of a slave.”
“Esca and I—” Marcus began, and broke off. He was not going to make a circus show of his innermost feelings and Esca’s for the amusement of such as Tribune Servius Placidus. “Esca has been with me a long time. He nursed me when I was sick; he did everything for me, all the while that I was laid by with this leg.”
“Why not? He is your slave,” said Placidus carelessly.
Sheer surprise held Marcus silent for a moment. It was a long time since he had thought of Esca as a slave. “That was not his reason,” he said. “It is not the reason that he comes with me now.”
“Is it not? Oh, my Marcus, what an innocent you are; slaves are all— slaves. Give him his freedom and see what happens.”
“I will,” said Marcus. “Thanks, Placidus, I will!”The beauty of this is that both scenes hold exactly the same content. Both are about a wounded ex-soldier hearing about his father's legion's lost eagle and deciding to take his slave on a quest to win it back from the wilds of Britain.
What the filmmakers did - which, frankly, I think is brilliant - was to keep the story the same but change the relationship between Marcus (the ex-soldier) and Esca (the captive slave).
In the book, Marcus and Esca share an instant connection, and have to figure out how to navigate being friends around the boundaries of their different cultures and baggage. Marcus doesn't understand Esca, but watching him try earnestly is rewarding enough to carry us happily through the book. There's this wonderful line about walking in without leave near the beginning that really encapsulates the slow burn of their relationship:
He never asked about those days, nor how Esca had come into the Calleva arena, because something about his slave, some inner reserve, warned him that to ask would be an intrusion, a walking in without leave. One day, perhaps, Esca would tell him freely, but not yet.(Amazingly, this is not a romance. I think. But they do settle down and build a farm together and never marry I AM JUST SAYING.)
In the movie, Esca is bought for Marcus against his will and they bond in spite of themselves: Marcus is bitter about his discharge from the army and Esca is bitter about being enslaved. We the audience see that these two men are kindred spirits, wounded fighters struggling to find a purpose in life, and over the course of the movie we watch as they slowly come to this realization themselves. The movie is also much more intense, which fits an action-packed hour and a half as opposed to the leisurely stroll we take through the book. (I'm just sayin, there isn't any tearful, "I thought I lost you," in the book. And yes that actually happens. God, this movie was marketed so poorly.)
Both are valid interpretations of a relationship between two unfortunate but noble men, and notably, each is more palatable to the culture it comes from. Mid-1900s Britain (where Rosemary Sutcliff wrote) understood the fatalistic nature of two men who could accept a rough hand dealt to them and keep pushing forward. America circa now might not get that attitude, but two bitter characters who find solace in each other despite themselves... well, you can see how that might resonate.
All this is to say that, while there are a hundred thousand ways to mess it up, it's also possible to make a good, valid adaptation that adds something to the source material. Personally, I prefer movies and books like The Eagle that allow me to look at the source material in a different way... but that just leads me to the zillion and a half incarnations of Sherlock. And I don't want to get into that.
Tell me what your favorite adaptations are in the comments! :D