In short, this book only reveals Nozick's philosophy in the few places where Feser stops trying to sell libertarianism.
The book starts off with some strong and helpful distinctions--such as between practical and principled libertarianism. Those kind of markers are nice to have. Later on, he also makes a clear (and helpful) distinction between the types of end-states and the types of historical states. The problem is that Feser doesn't stay true to his task--which is to write about Nozick. The helpful instances I just mentioned are few and far between. Instead, he more often introduces some topic from Nozick, then quickly strays into libertarian discussions.
For example, of the first 41 pages (over 40% of the whole book) very little is said about Nozick. The reader can go page after page and read nothing about Nozick. Instead, we are exposed to repetitive and abbreviated discussions of libertarian thought, much of which goes well beyond Nozick's project. Personally, I know that libertarianism has much to contribute to political theory, but that's NOT why I bought this book. I bought it to learn Nozick's political philosophy and get some critical analysis of it. The Wadsworth book _On Rawls_ by Robert Talisse, for instance, is much more helpful and balanced. I wish Feser had used it as a model.
Reader, if you want a better introduction to Nozick, read Jonathan Wolff's _Robert Nozick_ by Stanford Press. He is not a Nozick devotee, but he is fair to him. Then, if you want to clear up a few things or get a libertarian view of Nozick's thought, go to the library and check out Feser's book. It really is not worth buying, in my opinion.
On Nozick is a clear, lucid and well written account of the political philosophy of Robert Nozick. Feser sets the stage for Nozick's appearance in the history of libertarian thought and gives an accurate display of his own take on libertarian political philosophy.