"The Sisters" is a few firsts in Bette Davis' filmography. It's her first film with Errol Flynn, her first film with director Anatole Litvak, and more significantly, is her first film after "Jezebel" and its director William Wyler, the man who, in my opinion, made her a great cinema actress. It's also a film where the productions values are the best Warner Bros. was willing to give their rising money maker.
It's also a first for me - it is her first 1938-1946 film which I didn't like. And the main fault lies in the script. I never read the book which the film is based, but I expect is a mamooth melodrama in three volumes (even if it's only 200 pages). It compares the parallel stories of three sisters during the years 1904 to 1908, from US election to US election and catching the 1906 San Francisco earthquake. And here lies one of the problems. Our interest lies solely in the Bette Davis/Errol Flynn story, and the rest is (bad) filler. Particularly bad are both actresses playing the other two sisters (one of them would play Bette's daughter in "The Old Maid") and the parents' reactions to their daughters lives, more appropriated to 1938 than mid 1900s - they seem to take very lightly the elopment of one (despite the fact she married the man in question) and the multiple marriages of another.
Davis and Flynn do their best with the script, but both were able to do so much better, and I think Davis' dislike of Flynn comes from this film rather than "The Private Lives of Elizabeth and Essex". But there is one good thing that came out of the film. The outtake which comes up at around 1:50 in the video below.