The problem with reviewing this book is that although stylystically interesting, well written (to a degree) and certainly comprehensive, it is not the definitive introduction to philosophy it should be. As other reviewers have testified, this book was enjoyable and gave them insights into philosophers they may not have heard of. Indeed, I often refer to it when I come across some thinker I'm not familiar with.
However, there is a serious problem with this book. Russell is the first to admit that he doesn't understand some of the philosophers he covers, but some of his treatments are just plain wrong. If you tried reading this as an introduction you could end up with a seriously skewed view of many of the philosophers contained within - especially the more recent ones.
I would therefore recommend this more as a reference book for those who have studied at least a little philosophy, so that Russell's more ridiculous claims can be safely skipped and his arguments rated against those who have interpreted the philosophers in question more favourably. It is interesting to compare Russell to Rawls, who thought that one should never try to prove oneself more clever than the philosopher one was explaining.
Finally, not wanting to turn this into a Nietzsche argument, stating that Fascism is the 'logical conclusion' of his arguments is grossly misguided and shows the basic miscomprehension which surrounds this insightful thinker, and which this book in particular only serves to add to.