It seems to me that if you are looking for a film of the Shelley novel, stay away from the Mel Brooks creation until you are fairly familiar with the text or the story. I think that watching the 1994 version with Kenneth Branagh and Robert De Niro might be a good start. Naturally, reading the text in conjunction with the film could help you develop a better understanding of both and be able to make serious points as to where the film succeeds and falls short or where the novel surpasses. After this, I would suggest watching the Mel Brooks version. I think that his sardonic style and humor can be fully appreciated when understanding his targets. Certainly, some of the jokes can be grasped without full understanding, but a more meaningful humor experience would be present if one were able identify where his jokes are and the text would be a good set up for this.