I'd have to say that this film, though sometimes just shamefully manipulative for audience reaction (and I say that sort of as a compliment), is one of De Palma's very best films, both artistically and just in sheer entertainment value. It's got the low-budget quality of an AIP production, but set apart from Roger Corman's films or other films from the company. It's got such a strange, occasionally off-the-hinges, but dedicated wit that it's hard to ignore. In fact, this wit, and a good number of tight, screwed-up close-up angles, special point of view takes, and some of De Palma's trademarks (split-screen, ambiguous villain, women in trouble, etc) are what set it apart from being a complete Hitchcock homage.
It's no doubt that the director is so in love with the Master's style that, apparently, he even times his edits and shots to go with Bernard Herrmann's music. But what sets Sisters apart from even the more macabre Hitchcock films is that since De Palma is working in a low-budget, under-the-radar, with actors with not much credit to their names, things can be taken further than usual in dealing with the psychological 'whoas' of what goes on. This is possibly one of the most morbid tales to be told in 70's cinema.
Another important aspect to Sisters and its success is the faith that De Palma has in his actors/friend Margot Kidder and Jennifer Salt. They fit their roles so well one can't imagine big-name actors doing them any better (though Salt, up until the last act, is playing it all appropriately one-note). Kidder's Danielle/Dominique is quite a character too, one with so much complexity her story becomes like some wild ball of string that gets unraveled with little blood-laden marks along the road. Danielle brings home a truly nice guy, Phillip (good character actor, Lisle Wilson), sleeps with him, and then goes ape when she doesn't get her medicine...or is it her sister, Dominique? This first half hour is like some kind of satirical, sincere kind of film-making that could make just a great, open-ended short film. But with the addition of De Palma's split screen (possibly the best he's used it in any of his films), the story spins off into Grace, a reporter who gets on the case on her own to find out what happened to the body. This leads her into a very dark place, one that leads her into something so bizarre I dare not mention here.
But those last fifteen-twenty minutes or so are where things become a kind of make-or-break test in a sense for the audience; how far can one push this overtly surreal quagmire of a scene where the 'doctor' is present in front of our two main actresses? The 'doctor' himself is played by William Finley, and it would be arguable that his is such a toweringly creepy, scary performance of a villain that it becomes almost too uncanny. In this climax one has to wonder how far it will go, and then it becomes clear that it's almost the point of the story to go over the edge like this. We're dealt with an already peculiar premise of two Siamese twins, one of whom may or may not be alive, and how they're let loose onto the world. Early on it seems like this might just be an off-beat, funny noir kind of story, but by the end it becomes a bit more.
It takes originality to pull off some of the scenes here, or at least faith in what's written will work on screen. In a way this is the best place to see the bridge of De Palma's early black comedies (Hi Mom, Greetings; the neat opening TV show scene brings this to mind) and the hit or miss thrillers that have dominated his long career. Basically, for me, this was a hit, and that it was manipulative, sordid, and left the viewer still wanting some answers, makes it as successful a wink (if not homage) to Hitchcok that the filmmaker has done.
