Mmm I don't see any dichotomy between book and film. They're different cases of representation. An artist must not focus on what he's trying to represent alone, but on his representation of it; that's the definition of art for me.
http://en.wikipedia.org/wiki/Representative_realism
http://en.wikipedia.org/wiki/Representation_%28arts%29
And so book and film use different tools to get a representation into our minds, some artists prefer one of the two and we as audience like to enjoy both. But just like they're different so are different genres within a single art, such as painting.
You can't compare a film with a book, and I agree with Rlbell that the worst way to adapt a book into a film (or the other way around) is trying to deliver the exact same message *in form*. And it's wrong to criticize a work of art, or compare works of different arts such as literature and cinema, by how close they are to the reality they represent. First of all because we can't, everything we know and think about is representations of reality, never reality itself because we apprehend it always through a representation, even when we see it with our own eyes.
(That's why I find so funny that so many people judge the quality of a book by how accurately it describes things and specially the stage, they think good literature is about including photographic descriptions (with good adjectives) of every place. Many times there's a point in descriptions but that's just ridiculous and opposite to the way to go. If an author is doing that he should be making a movie.)
Well in short I do not think one art is better than other, or more meritorious or more noble or even requires higher mental skills to enjoy. Of course there are films that can brutalize or at least don't cotribute anything to the audience; but if you think about it there are also many like books.