What is your opinion about the book "The Natural Way to Draw" by Kimon Nicolaides? I have read some reviews that say that this is the best "how to draw book". Now I have it but I am not quite sure whether I should undertake it. If I spend 3 hours a day doing the exercises in the book I will not have much spare time to draw anything else. And I am not sure all the exercises in the book are really helpful.