Considering the subject matter at hand, the authors have done a tremendous job making it accessible to the average person. Some prior knowledge of the principles and jargon of investment is required, but not so much that you cannot pick it up as you go along.
Time and time again the principles within have been proven correct and true, most critically when the professional consensus has been to consider them out of date. The book promises less than other titles on investment theory, and for this reason alone it is often held up as a symbol of an unrefined and primitive form of investment theory.
Personal experiences vary, but what cannot be refuted is that each edition that has been published has included new statistical data covering the interim period. Each time that data has shown Benjamin Graham's method of analysis applied to value investment to have been reliable. Indeed, even throughout periods of major economic booms and busts, the principles have been demonstrably correct.
The simple facts of the truth are a powerful advocate, and nothing more really needs to be said about this book.