I was disappointed with this book because the author is slow in getting to the main topic. The total length of the book is 287 pages and the discussion on global democracy doesn't begin until page 219.
After an introductory part I the author gets to part II, which actually constitutes half of the entire book. It's a presentation of the history of the modern state and modern political systems. Not bad as a broad outline, but it's also obvious that the author is no historian. He merely skims the surface of state history with a detached theoretical perspective. Frankly, I don't see any reason why half the book should be used on a historical presentation which isn't of any relevance for the theoretical arguments at the end.
In Part III we finally get to democratic theory. But once again the author exhibits poor judgment. He spends a lot of pages on the principle of autonomy and on democratic thought experiments. These are quite abstract questions in democratic theory, and the author fails to explain their relevance for cosmopolitan governance. Spending another 70 pages on them seemed a bit pointless.
The author performs better in part IV when he at last gets to cosmopolitan democracy. This part was worth reading, but I was still mystified by the author's emphasis on "autonomy". His basic argument is quite simple: personal autonomy should be enforced on a global scale by international democratic law. If we can implement global democracy, we can effectively protect human rights, freedom and justice. This isn't exactly a deep insight. Constructing an abstract "principle of autonomy" and saying that it would be good if everyone could respect it, isn't an interesting argument. The author does offer some ideas for institutional change in international politics as well, but they don't amount to much more than pure fantasy. Perhaps he could have argued his case more convincingly if he had extended his central argument to 200 pages instead of 60.
In conclusion, I think this book is poorly structured: the preliminary parts are too long and the argument is much too short. But if you're looking for good books in democratic theory, you might want to consult this book just for its bibliography, which is quite comprehensive (up to 1995).