It's also important to judge the movie on it's own, but that's not an excuse for filmmakers to betray the spirit of the book.
What does that even mean, really? The "spirit" of a book is such a vague idea, that it can mean many different things to many different people, for the same book.
The movie has to be translated, because it's a different medium. Has there ever been a movie that was exactly like the book? No. Of course not. Because you can't. You literally cannot make the movie the same as the book. Well, in translating from one medium to another, there's a lot of room for interpretation, and how one filmmaker sees the story will never be the same as how another sees it.
You can say you wish they would've include this, or you wish they wouldn't have put in that, but you can't reasonably say that one is better than the other, because they're two completely different things.
I think the Eiffel Tower is better than Muhammed Ali. And skateboarding is better than the moon.