If you just use your common sense you know its not gonna work.

The Godfather: Great movie. Entirely based on the novel

The Godfather Part II: A bit less than The Godfather, but alot of people disagree, won more awards. Bigger budget, more freedom for the director. Only halfly based on the novel.

The Godfather Part III: A lot less than The Godfather and The Godfather Part II, the chances of being made were slim, very slim, Nino Rota died, so no knew themes, just oporah, and themes by Carmine Coppola. Not based on the novel at all. A lot of the original collaborators didn't join to make it, because it was 20 years after The Godfather.

The Godfather Part IV: No help of Mario Puzo, again no new really good music themes, alot less collaborators than The Godfather and The Godfather Part II. Probably gonna be a lot worse than The Godfather Part III.

NO GOOD IDEA!

P.S: Correct me if I'm wrong.