Here is an overview of the criticism I've seen about preparation resources thus far.
- On one hand, 3rd party resources are a serious problem because they do not, and possibly cannot, successfully mimic questions from the original exam. Some are even reportedly biased to support their own (often crazy) strategies;
- On the other hand, the makers of OG have little incentive to teach you efficient strategies to explore loopholes in the actual test, which means OG will only take you so far. I haven't seen debriefs of successful test takers that prepared only through OG;
- Furthermore, most people who score high on GMAT are already proficient at the test subjects. They only use these materials to adapt and hone their skills as needed. They are usually fresh students from certain graduation courses or very experienced professionals from top level management of large companies and like. Exceptions as to how you may acquire such proficiency are rare. Therefore, these debriefs may not be a reliable indicator of resource effectiveness;
- Indian IT guys in the mid 20s are the prevalent profile of the GMAT test taker. They are proficient at quant skills but have a hard time with verbal. Because of the greater demand for verbal training, most discussions on forums, course offers and discounts, study plans, and the experience tutors acquire over time, tend to be tailored more towards covering the verbal section, so people with a math skill deficit will have an even harder time seeking help.
I've found it important to make these observations available to everyone so people can contribute or question them. Might even be some will find it useful.