I bought Kaplan's GMAT Premier 2014 after a disappointing experience with Princeton Review's Cracking the GMAT book, and it fulfilled most of my GMAT studying and review needs. Just a little bit of background information on me: I'm a native English speaker, so I didn't have too much trouble with the verbal section, even before going through these books, but they did help boost my score a bit, especially in reading comprehension and having a strategy for the writing assessment. I've been out of college for more than ten years, but in college, I used to tutor math, so I did know most of the GMAT math at some point, even if I had forgotten it by the time I started to study for the test. I'm not the type of person who tends to do extremely well on standardized tests.
This was my GMAT studying experience: Overall, I spent just under thruee months studying for the exam while working full-time. I usually studied 20-60 minutes most weekdays and 2-4 hours most Saturdays and Sundays. I went through the Princeton Review book over the course of a few weeks, and my score increased from about a 550 to a 600 based on their practice tests, even though I felt like I thoroughly understood most of the concepts in the book. I bought the Kaplan book, and I did worse on the diagnostic than on the Princeton Review tests, which made me think the PR tests were too easy. The verbal section wasn't a problem for me, but even after going through the whole Princeton Review book, I was only getting about halfway through the Integrated Reasoning section and two-thirds of the way through the quant section before time ran out, so I definitely wasn't satisfied.
I bought the Kaplan and went through the book over the course of a few weeks, doing the problem sets as I went along, and taking a full-length practice test every two weeks to make sure I didn't forget too much of the previous material. I had no major issues in the verbal section from the beginning, so I spent a lot more time reviewing the math and writing down key formulas and points I needed to remember. I did worse on the second test than the first test, but I noticed that I was missing much harder questions that never even appeared on previous tests, so it was progress, in a way. I took a final practice test after finishing the book and scored a 700, with significant improvement in my quant score. I was aiming for a 700 and probably would have been satisfied with a 650, so I took the GMAT a week later. I ended up getting a 740 on the GMAT (47q, 45v, 7ir, 6awa), much higher than any of my practice tests. This leads me to believe that the Kaplan practice tests are harder than the real thing, but not to a ridiculous degree. The real test still had most of the same types of problems in the book, but they were often slightly less complicated.
My only complaint is that each section has so few practice problems. I wish they had more practice tests for each type of question, either in the book or online. Instead, it seems you are limited to long and generalized practice, which may or may not include a few of the question types you need to practice.
Overall, I highly recommend this book to anyone who is in a similar situation as I am. If you're not a native speaker of English, it probably won't be good enough. Also, if none of the math in the book even looks familiar to you, you may want to start with more basic books. However, if you vaguely remember doing this type of math in high school or college, this book is probably a sufficient refresher and will help a lot with strategy.