that's not necessarily correct. as contradictory as it seems, from an academic standpoint the most important thing about a book or other work of art may not be its technical achievement but thematic or historical value. for example consider japanese literature, one of the most "important" books is something called "The Tale of Genji" which is a for lack of a more apt description a comic book. what's significant about ToG is the fact that it portrays with such vividry the courtly life of that period of japanese history. a more acessible example would be shakespere, who although now revered, was in his time considered a hack, a close contemporary analogue for his plays would be what you'd see on UPN these days... quick sets designed for the masses using common gimicks and known gags that now seem intricate and sublime but mainly due to the fact that few extant works exist today from that time. was Casablanca a great movie? was Gatsby a great novel? both were panned critically for techinical merit upon release but have both proved worthy in the eyes of most readers and moviegoers

in the case of TGF, although it's the rare case that the movie is much better than the book, the HEART of what makes the movie great is stolen whole from the book. the themes of family, honor, vengence, loyalty etc that makes TGF the most important movie in history sprang not from Coppola's head but from Puzo's. the breathtakingly daring and plain never-before-done perspective of a humanized mob life from the eyes of the family which proved so influential in both literature and movies also sprang fully formed from the book. it's not a pretty read but Puzo's TGF is undoubtably a great book