I don't really value the faithfulness of adaptation in and of itself. There are things that books do really well (interior dialogue) that is very tricky to translate to screen, and can frequently be quite clunky in execution. Similarly, many of my favorite scenes in films cannot be adequetely articulated in prose.
I don't think that either Godfather or Exorcist are faithful at all, to the benefit of the films.
I feel pretty much the same.
Also, and I don't know if it was in this thread it was addressed but it is still related to what's being discussed here regardless, but I don't quite believe much in the uncontested wisdom that 'the book is always better than the movie'.
Um, no. More than regularly, this is proven to not be true by how many terrible books have been turned into good movies, but also I don't even agree that books are by default a superior medium. As stated, they can do some things movies can't. But movies can do some things they can't. And I don't know why any of these particular things should be considered better than the other.
Because books=smart? Nah. Look at the list of best sellers since, I don't know, probably the dawn of time. Books are pretty frequently just as 'dumb' as movies.
Now while I doubt any film adaptation will ever be as good as Dostoevsky's "Brothers Karamazov" or "Crime and Punishment", and any writing of Dickens cleans the floor with even its best adaptations (with the exception of Scrooge), and let's not even get into Gravity's Rainbow and how it would be dumb to even pretend that should be adapted, the kind of books that really use the maximum potential of their medium are few and far between. I'd stipulate that most 'great novels', in the right hands, could quite possibly be turned into movies that are greater. Because why not?
I assume for many (I suspect I may even have said it a few times myself in the past), the reasoning might turn out to be "Books allow me to use my imagination, and that's better than anything any director could show me?" All I can say to this though is another "Nah". I think we give ourselves too much credit when we say this. Maybe that's what makes it feel so good to believe in this idea that books are unmatchable in their greatness. Because we can claim some amount of authorship over them.
Or maybe they really are that much better, and I'm a big dummy and am reading all the wrong books. I'm certain one of these reasons is definitely more likely than other.