Creepy and effective thriller based on atmosphere and ambiguities (spoilers)

Rating: Null/10 (21 June 2004)

Rosemary and Guy are newlyweds who move into a new apartment in an old building. They meet and befriend the elderly couple next door, the Castevet's, who are very friendly and make them both feel welcome. After Guy's acting career suddenly turns around and he lands quite a big role (due to the original actor going blind suddenly) the couple decide to try for a baby. They plan the night that they will try on both Rosemary gets drunk and passes out, dreaming of some weird rape-like attack. She awakes the next morning to find that Guy had just been drunk and had had sex with her anyway  but she forgives him when she finds she is pregnant. However with both Guy and the Castevet's acting strangely it appears that something strange is going on, or is it just a frustrated Rosemary's over imagination?
Of course, many of us know the answer to this question; even those who have not seen the film will know that things are not just in Rosemary's head, however what makes the film so creepy and enjoyable is the fact that Polanski doesn't seem to want to make his mind up either and plays it right down the middle. As such the simple plot sees lots of ambiguity in the story for much of the story, although we are pretty sure something is going on the director never comes right out and says it, instead he continually suggests it while also pointing to Rosemary's mental instability. It is the confusion in Rosemary that makes this so creepy and engaging  she herself goes between disregarding her fears and embracing them and it is very effect in building the tension even if we know what is the truth (or else there wouldn't be a film!). However, even though we know what is coming, the end is still very creepy and I was surprised just how effective it was even on a second viewing.
The story builds a nice conspiracy well and sustains a real creepy atmosphere all the way through to good effect. The performances are also key in pulling off Polanksi's trick. Farrow is suitable unbalanced and we feel her fear and suspicion growing during the film. Her performance is really good and the fact that she manages to balance her own doubt for most of the film is very effective. Cassavetes is also excellent, all at once he is friendly, cheerful, menacing and mysterious; he also plays a big part in creating the sense of doubt that drives the film's tension. Ruth Gordon is a nightmare neighbour and overplays very well even if her character is a bit of a cliché  I certainly would not want her for my neighbour, but she is never so creepy that we know for sure, only overbearing in a normal yet weird manner. Likewise Blackmer is effective as the potential head of the coven and is never too obvious to blow the tension. The support cast are all good and echo the performances of Blackmer and Gordon.
Overall this is a great horror thriller. Another review on this site has rightly pointed out that too many modern films in this loose genre will have a vague tension over poor dialogue delivered by a 'teen-friendly' cast and then tonnes of expensive effects. Happily Polanski is smarter than that here and he uses doubt, tension and atmosphere blended with good dialogue and some fine characters to create a film that is never really scary so much as it is just creepy. Even though I know it inside out it is still effective and it doesn't bode well for modern films that rely on effects instead of these qualities.