Rating : - "THE" book for GMAT
No matter what you read or don't read, this book is a must for all those who prepare for GMAT. Though some of the explanations/concepts are not so well written, this book has the "REAL" content. Most of the questions listed in this book are supposedly taken from previous GMATS. And that explains why you see such a similarity between problems/questions in this book and the real GMAT ones.

Having said that, just this book alone will not be sufficient for most of the people as there is a very less emphasis on explaining the basic concepts. I recommend using Princeton and/or Manhattan series books as a supplement to brush up the fundamentals and then use this one for practicing GMAT-like questions.