The essence of the book was completely left out in the film
The film doesn't make justice to the novel at all.
Julia's character does not have the same complexity as it does in the novel.
Many key moments in the her relationship with Tom are concentrated into small scenes that make her seem too wick and not too clever either.
She is in fact a double persona, the one she lets other people see and the one she really is.
Also, the most important scene in the hole novel and for me personally ( her discussion with Roger after his return from Viena, where he tells her the most infuriating truth about herself, which is that she in fact had no personality of her own, that she was the sum of all her roles and that she only played the role of a loving and caring mother, the role of a great actress, the role of a faithful and devoted wife, etc and that many times he was wondering "When I've seen you go into an empty room I've sometimes wanted to open the door suddenly, but I've been afraid to in case I found nobody there."
The function of art is not to serve as example, but to harrow his soul.