I think that the article once more underrates the novel. It's true, some of the memorable lines like the cannoli-phrase were added (the first one improvised by Ms. Sheridan-Castellano, the latter added in the studio), but the novel contains some strong lines too which provide a certain drive to the story. For example: "A man has but one destiny."
This line makes the story look like an ancient tragedy: The young hero struggles hard to not become like his father. But the more he tries to escape his fate, the more he is drawn into it. No-one can escape: Sonny, Fredo, Kay.