I bought this book because I'm getting more and more involved with computer graphics programming and I was interested in digging in something lower-level like OpenGL. I am no professional programmer, just hobbyist, I know python fairly well now and am just beginning to put my fingers into C++.
So, what I wanted was basically understand how OpenGL works, be able to follow with my limited C++ knowledge and also get a couple of yummy and well organized pieces of code to explore. This book fullfilled those 3 topics perfectly.
Some of the critics the others reviewers made may be true, for ex. that the example code doesn't correspond exactly to the examples in the book, but I didn't find that a bad thing, I saw the code more like "real-life" examples to explore, practice & tweak after you learned some theory in the book.
My very small knowledge of the C++ language didn't give me too much problem, the book focuses on explaining how you do things the opengl way and not on building working programs. For example it says things like "In OpenGL, this is how you must build a triangle: you first build an array with the vertices coordinates, then pass it that way". I had a bit of difficulty understanding a couple of specific programming topics at the beginning of the book, but the author himself doesn't extend much on those parts.
So I think you must not consider this book as a practical manual for building games, but rather a theory book about openGL, but a theory book made with a quite practical approach. It doesn't talk much about 3D geometry itself, but focuses on making you understand "the OpenGL way", with small tricks, examples, and the well-known experience of the NeHe people. If you already know a bit of spatial geometry (how 3D coordinates work, how vectors work, etc), it will help you greatly.
After reading the book my idea about OpenGL is that it is really, a bare, salty and undigest piece to eat. Everything must be done a certain way, not another and it is sometimes very counter-instinctive. But I also realized that OpenGL is the true foundation behind almost any other higher-level application, library, method, game or anything else realted to 3D that I have encountered. Things I encountered in some games, in Coin3D or in Blender suddenly make sense. I knew how you apply a texture on an object with your favorite 3D app already, but I know now how it works internally, and I have a good idea on how I could write a shader myself to overwrite the standard way...
So I enjoyed much this book, and probably will come back to it often as time passes.