“One thing you can count on more often than not is that the book they were taken from was better.”
Only exception to your rule that I know of was “Jaws”. The movie was much better than the book.
I will give you that, the movie was better, but I have never been a big Benchley fan. And while I am NOT a big fan of L. Ron Hubbard I do consider Battlefield Earth to be a great read. It is so vast in scope and somewhat campy in a Buck Rogers sort of way. It was as if he used the unoffical sci-fi story formula of the 30’s or 40’s. Could not be done in a movie unless it was many parts, like Star Wars, or a long tv mini-series like The stand. As to Soylent Green, if I recall correctly it was originally a novel by Harry Harrison called Make Room Make Room. The book had the story of the murder, the crowbar used and all that. But the soylent green was just food and had no connection to anything at all.