This is a very good book; topics are presented in the right order and chapters are well written. The book is not an OpenGL manual (and it couldn't be, as OpenGL documentation is very long). Instead, essential OpenGL commands for each topic are mentioned, always with one or more small examples, which I found very useful. I would prefer a few sub-topics to be more emphasized, but this is a minor remark.
Small program chunks, aiming to emphasize on details or surprising results are often included, and help the reader understand the topic more deeply. Longer examples, usually one or two pages long (and well commented), are also included. In general, the book is full of examples with high educational value.
The book is written in such a way that It is quite possible to read only the chapters you are interested, skipping others. However, I would recommend not to skip Chapter 3, which introduces essential information concerning modeling and viewing transformations; this requires some decent knowledge of vector algebra, but it is inevitable if you really want to understand OpenGL.
The book uses a "moderate" level of C/C++, avoiding very complex features of the language, which makes the numerous examples in the book easy to understand. As a plus that may or may not count for you, Open Source software is the driving force behind this book. Also, the book is considerably cheaper than most of the books concerning OpenGL.
It is nor easy for me to rate a book with 5 stars, as I expect a lot from a book. In fact, this is the first time I rate a book with 5 stars, and there is a good reason for that. All in all, I would highly recommend it. If you can't understand OpenGL after reading parts of this book, I doubt you will ever understand OpenGL.