For me, there are two key assertions in Robert Adams' "Beauty in Photography". First, that we "live in discouraging hours of society's apparent decay" (p. 88). Second, that the purpose of art is to "help us meet our worst fear, the suspicion that life may be chaos and that therefore our suffering is without meaning" (p. 25).
From these two assertions Adams develops his interpretation of photography: Photography detects, extracts and emphasizes the beauty around us, and by doing so it points toward something deeper in the world, an organizing power, a coherence supporting the world and our lifes. To Adams, photography is a spiritual exercise, making bearable an otherwise decaying sourrounding.
Art not concerned with depicting the world beautifully is, to Adams, mere "decoration". Thus, Adams tells us little interesting about most modern art, and his approach does not generalize, for instance, to music. That beauty can exist as such, that it can tell us something about ourselves even without refering to things in the world: This does not seem to be Adams experience.
In these very conservative views I disagree with Adams. Still, I recommend his essays to anyone who wants to understand why some photography is moving us while other is not. Even if Adams is not telling the whole story -probably nobody will- he is an excellent writer who talks about art in a clear and understandable way.
The only disappointment with the book was the poor reproduction quality of the images depicted. As a publisher specializing in photography books Aperture could do better.