It's suppose to be the book version of his classes which were praised by Bridgeman, Rockwell and Frank Reilly. Rockwell was supposed to have sat in on Nicolaides classes several times even after "making it".
The more recent "Force" books is most compared to this one book, as the focus on weight and mass of the subject is the primary goal.
You'll see a lot of beginner artists pick it up and drop it within the first 5 chapters, because of how much time is expected. The original classes were designed for students who were expected to draw for a majority of the day. 3 hours on these lessons and another 6 hours on two other subjects and 3 hours for personal work. Most of the beginner artists today don't have that sort of routine available to them as they have their own assignments or work that gets in the way. So they use this as their sole curriculum and get bored quickly, which is fair considering it's suppose to be only one part of a daily curriculum.
