I got the Understanding Exposure book from the library, it terrified me! Made me appreciate that as far as technicalities goes, I know pretty much nothing about photography. Didn't enjoy it myself, each to their own I guess but I prefer learning the camera etc through excessive practical application, and then learning about composition/being inspired by photo books (i.e. just books full of photos, not technical stuff)
Probably says more about what sort of a photographer I am than a fair assessment on the actual book, but I would probably feel like I'm learning more from looking at something like
this, and then fumbling around trying to do something similar myself.