I wonder if the movie would be as good if I had watched it before reading the book, but, I guess, I wouldn't even be interested in watching the movie if I hadn't read the book first. It comes to mind that the movie was actually made for those who had actually read the book, as the movie does not make obvious references or introductions to a few secondary characters (which again, were described more vividly in the book). The small conflicts, the questions, the vivid characters enjoyed in the book are sadly diminished or even non-existent in the movie, but a reader would recognize the main story plots to keep the story recognizable. Granted, adaptation of a book to screenplay is one of the toughest jobs out there, and not even the author himself might of made something better than a professional screenwriter. But in all aspects, both the screenwriter and the director did a fair job in bringing the story to the silver screen, and the casting was great (although I thought Momma would be older than depicted in the movie), and they dared modifying certain details of the story, and even taking the ending further than the book, to keep it interesting.
But the sheer strength of the original story (and all its symbolisms) still take What's Eating Gilbert Grape? into a great movie. Applause for the screenwriter, and the cinematographer.