Out of the three books I used, this book gets my highest rating. The other books I had were Kaplan GMAT (2005 Edition) and the Official Guide for GMAT review (10th Edition). I ended up taking the test twice. Studied for about 4 weeks before the first test, mostly using Kaplan book, as I heard it had the hardest questions (and was the lightest one to carry around in my bag). Practiced on Kaplan's computer diagnostic test, and got 540. I feel, they make their material unnecessary hard, probably to make you register for their prep course. Spent some time reading Nova's book, and found it much easier as well as providing much better explanations. Also questions were much more in line with questions from the Official Guide. Took the test and got 650 (q:48, v:31), and was very much disappointed, mainly because I didn't do a good job pacing myself on the verbal section, and ended up not answering the last 5 questions. I knew I had to study and concentrate on Verbal section in particular, because I felt that I had to guess on almost every question in that section.
This time, I only used Nova's book; Kaplan was put aside for good. I just read the Nova's book from start to finish doing almost all the problems, and getting to the bottom of every explanation. Two days before my second test, I just reviewed their summary of math problems, to make sure I still remembered some basic formulas.
Got 700 on my second test (q:49, v:35), and I am sticking with that score. English is not my first language, and Sentence Correction must be my weakest area, and no GMAT prep book will cover all the rules and idiomatic expressions. But for Reading Comprehension and Critical Reasoning, explanations are clear and well structured covering all possible question types, and the approaches suggested by the book helped me a lot on the actual test.

I am very happy with this book. After reading numerous reviews about this and other GMAT guides, I chose this one. It was not easy to find in bookstores, which largely carry the more familiar titles(Kaplan, etc.) I bought the book around Christmas.

I felt pretty rusty with much of the material(I've been out of school for a while), so I started working my way through the book a little at a time, somewhat haphazardly. Then I actually registered for the GMAT three weeks ago, and suddenly my sense of urgency got more intense.

Now then, the review:

I found that the coverage of the mathematics topics and the verbal topics to be thorough and comprehensive. I was able to re-familiarize myself with the material pretty quickly, and my performance on the test questions in the book improved a great deal. Similarly, I was able to improve my performance on the Verbal questions, although I found that section much harder to get into. This was more a function of the material than the writing.

To my mind, the greatest value this book offers is not the mathematics or grammatical reviews, but the test information that it offers. The factor that improved my scores on the Powerprep tests more than anything else was the dissection of the test, the explanations of the questions and how to answer them, and other test strategy information offered by this book.

If you just read the sections on the types of questions, what they are looking for, and how to attack them, you will improve your scores a lot. This is true of the essays as well. Once you memorize, or at least practice, the formulas for how to write the essays, you will get past the fact that the topics are stupid and pointless, and will be able to write a good essay despite the amazing banality of the topics.

The result: I got a 690 on the GMAT using only this book, and studying sporadically for a few weeks leading up to the test.

For reference, the first time I took Powerprep CAT 1(January), I got 34 Quant and 26 Verbal. On the Saturday before the test(February), I got 49 Quant and 36 Verbal. On the actual GMAT, I got 44 Quant and 41 Verbal. I give credit for the improvement to the test strategy and explanations provided in the book.

I highly recommend this book to help you prepare for the GMAT.

I used a total of five books in preparing for the GMAT: Barron's 13th edition, Petersons 2003 and 2004 CDs, Kaplan 2005, Nova's GMAT Prep Course 2003, and the Official Guide.

I have taken the GMAT twice. The first time I used the Barron's book and the Petersons CD and scored a 40% on math, 75% on verbal, and a 4.5 on the essay for a total score of 570. This score was unacceptable.

The second time around, I budgeted more time to study a day (around 6 hours) and for a longer time period (a month and a half). For me, I felt I had a strong background knowledge on all the required subjects, but I was not as honed on specific strategies and techniques for answering questions. My thoughts on each book:

Barron's: As a beginner, I enjoyed this book. I read the whole book and did all practice tests. They did not explain probability, sequences, and progressions questions well. In general, the math explanations were a bit sketchy. However, the word problem explanations were the best out of all the books.

Petersons: I just used the CDs and did not look at the book. After taking their adaptive practice tests, one is provided feedback which has questions divided into very difficult, difficult, etc. This is beneficial because you can see the level of difficulty at which you generally test. This is a really helpful addition that other CDs lack.

Kaplan: My least favorite book and CD. The book had very poor explanations for test questions. The book only offered general guidance for taking the test and outline common strategies. The cartoonish CD just became annoying and took more time than it was worth.

Nova: Far and away the best book. After reading reviews on various sites, everyone recommended Kaplan and Princeton Review, but no one mentioned this book. I found it by chance at the local book store. It covered everything on math and had exceptional, comprehensive explanations. Also, the drills after all chapters were very, very, very helpful. After doing all drills in Nova, the commonly considered difficult practice questions in Kaplan were almost a joke. I would recommend to anyone this book.

Official Guide: A must to have for everybody taking GMAT. I did the last third of the questions for each section, which are typically more difficult.

I recommend, in order from best to worst:

Nova, Official Guide, Petersons CDs, Barron's, Kaplan.

I recently took the test again and got a 96% in verbal, 60% in math, and a 690 overall.

I am a Professor of English, and I make double my salary tutoring on the side. I make it my business to find books and use them to help students get into graduate school. I have found the Nova book complete in every aspect. I don't have time to write this, so the fact that I did should convey my satisfaction. Furthermore, the student should have a complete understanding of the math and sentence correction portions upon completion of the course. Without unnecessary rhetoric, the text is exact, with comprehensive yet concise answers, in the math and verbal sections.This is definitely a three year crash course in a several month program. Lastly, again, as a Professor, the answers were correct, concise, and cutting to the point.To suggest otherwise, especially in the English portion, indicates the reader has a need of rudimentary teaching.

This book's mathematics review, depsite some obvious errors, is useful and provides a somewhat more challenging and more representative set of algebra word problems than does Princeton Review's off-the-shelf book. The sentence correction review, however, is poor: some of its answers are simply wrong (I speak as a former writing tutor) or are simply unrepresentative of the questions of the real GMAT. Princeton Review and Kaplan both provide far superior preparation for sentence correction questions.