UGH what a textbook. The CISSP exam is a soup-to-nuts memorization contest against all of the acronyms and other knowledge required to be an information security professional. So, the book is HUGE because it needs to be. Definitely buy this one as an ebook if you plan on taking the exam.
Compared to other textbooks, this one is pretty awful. Multiple related terms to the one being defined as always listed mid-sentence. There are almost NO illustrations or diagrams. Sometimes there are lists. Occasionally Stewart provides a good mnemonic like All Presidents Since Truman Never Did Pot for the OSI model, but most of the text is raw, unformatted paragraphs. No color ever. Dry as can be expected, especially in the hash algorithms section, but very few visual aids to memory and a horror to annotate if you made the mistake of renting a copy. I know, they cannot afford more trees to provide adequate white space or margins because it's ALREADY pushing 1000 pages, but they could certainly re-write it for easier reading and clarity.
The tests that accompany that book are thankfully free with registration. (No access code needed.) They are the same review questions as the ones that conclude each chapter, but sometimes it's better to take them online. I didn't get into the bonus tests, but those are nice to have too.