The content of the book provides a solid introduction to computer networks. The book is well structured and the chapters are well written and laid out thoughtfully. More detail regarding the nature of the principal communication protocols is incorporated into the material than other texts and as such probably provides a bridge between the novice and a seasoned professional more accustomed to reading RFCs. Each chapter is supplemented with problems to check comprehension of the preceding material.
However, the book is not without its annoyances. Appendices are referenced which are accessed online and are not present in the book itself. Having to move from a paper book to a digital appendix can be awkward - if the text were available as an e-book this wouldn't be nearly as bad. Some of the additional materials appear to be included as an afterthought with no apparent integration within an otherwise well-structured work. I suppose they could be useful to some people... certainly I found the SI prefixes document to be incomplete compared to freely available sources from an Internet search.
The book also boasts animations as a "powerful tool for understanding the complex mechanisms of network protocols". These are only made available via instructors... if the animation tools are so darned powerful, why not make them available directly to students? I make this comment without having yet witnessed said animations. I have raised this matter with the author, but perhaps I didn't make myself sufficiently clear.
Similarly, some of the end of chapter questions are open-ended. This is good if one is attending a course to receive feedback, but absolutely *awful* in an independent learning scenario, since there is no way whatsoever of checking one's answers.
Overall, I would recommend holding off from purchasing this book even if attending a course primarily due to the open-ended nature of the exercises. Any answers to these questions depend strongly on the dedication and competence of the instructor and cannot be derived from this book alone: see if you can use the library until you're certain of getting value for money. There are other texts out there which are classic (eg Tannenbaum, Comer) depending on the learner's background. Perhaps they do not always provide the enthusiasm and stimulation which Stallings imbues within his writing but they are self-contained works.