First, I want to take issue with other reviews here that suggest that Rousseau was dealt with too briefly in this book. It is, after all, a part of the Very Brief Introduction series. How else is he supposed to be dealt with? The book has some problems, but brevity is not one of them. One of the best books published on Rousseau -- and I mean one of the two or three most important works -- is Ernst Cassirer's THE QUESTION OF JEAN-JACQUES ROUSSEAU, which is considerably shorter than this book by Wokler. The problem isn't length, but what the author has done with the room he has to work with.
The problem I have with the book is that it is largely a string of disconnected bits and pieces without much success blending them together. The major themes in Rousseau's works were not clearly identified and it wasn't clearly shown how they flow through one book to another. Key ideas are brought up, but are not tightly connected with other ideas, so that it isn't made clear how all his notions tied together. But I do think that there is a sense by all of the reviewers so far that the book doesn't do a very good job of laying out Rousseau's thought.
I read this largely because I like to read one of the books in the Very Short Introduction series as I walk about doing errands (or just taking a walk -- yes, I have the odd habit of reading while I walk) during the work week. They are very light and easy to carry around and feel nice to the hand. I bring this up because it explains why I read this rather than another book in the series. If I were recommending to someone a good intro book on Rousseau I would recommend instead Nicholas Dent's intro on Rousseau in the Routledge Philosophers series or, if you are willing to read a longer text, THE CAMBRIDGE COMPANION TO ROUSSEAU edited by Patrick Riley is very good. Roger Masters's book on Rousseau's political philosophy is great, but out of print and extremely expensive used. And the book I mentioned above by Ernst Cassirer is definitely worth reading. But unless you are trying to read all of the books in the Very Short Introduction series (which I might actually be edging towards doing, just for the heck of it), I really can't recommend this as an intro to the thought of Rousseau.