It is hard to imagine someone coming to this film over 20 yrs after its release without an insight as to the core premise. If you are such a person, hold on. The performances put in by Norton, Pitt and Bonham-Carter are extraordinary in an atmosphere where the viewer thinks they know what is in store, but they are mistaken. Whilst criticised in some quarters as reinforcing the patriarchy and male self-gratification via violence (it probably does) the film is unapologetic about it - true to the book upon which it is based.
Brilliant - until the last act. It seems the screenwriter simply could not reconcile what had been created by the storyline and the climax is less then what the film deserved.