Galloway is a triple threat: he's fluent in the esoteric dialects of poststructuralist theory, Internet geekspeak, and network aesthetics. There are plenty of books that try to tackle the art and politics of the Internet age from one of these angles, and a handful that try two--but if you're looking for a three-dimensional treatment of the subject, this is the book for you.
Protocol's subtitle, How Control Exists after Decentralization, gives away Galloway's intention in writing this book, which is to steer a path between the "media are chains" intonations of broadcast media critics and the "networks make us free" hype of Internet evangelists. The fact that he's trying to erect a new theory in this uncharted territory makes this book a valuable contribution to the field.
Sometimes I think he loses his path along the way, as when he veers afield from his focus on networks to apply his ideas to an abstract "biopolitics" or to propose an aesthetic interpretation of Marx. None of these efforts is misguided or irrelevant, and academics with heads in the clouds will probably love these parts. Personally, however, I find Protocol most useful not when it connects one theory to another, but when it connects a theory to a specific technical specification. When Galloway pulls A Thousand Plateaus of the shelf to reveal the politics underlying the Internet's fundamental TCP/IP protocols, he's not just showing off his booklearning--he's upgrading Deleuze and Guattari's theory for use in the field, so we can apply their radical philosophy to the email and chat applications we design and deploy.
If you're a teacher trying to explain the relevance of dead European philosophers to students who'd rather be learning the latest PhotoShop filter or IM client, Protocol is a great translator between these realms. In my classes, I make them read an excerpt on a specific topic--network diagrams, for instance--but I also ask them to analyze the handy tables and photographs Galloway uses to condense and illustrate his points.
(Disclaimer: I know the author from our mutual work in the field of Internet art. That said, I know a lot of the authors of recent books on new media--it's the nature of the field.)