Roman Polanski’s 1968 film remains a classic even for those of us who think the horror genre plagued by a built-in, nagging silliness. After moving into a new apartment, an alarmingly fragile and doll-like Mia Farrow begins to fear that the jovial-yet-creepy old couple next door has weird designs on her unborn baby. Soon she begins to suspect that everyone from her crotchety new doctor to her increasingly jumpy husband is in on the “plot,” and the film turns into a unsettling parable about a woman beset on all sides by a world of smiling, friendly and deeply treacherous men. (Strangely, considering Polanski’s reputation, the film can easily be read as a feminist attack on a society devised to exploit and abuse women.) You probably already know what the “twist” is — which is a shame, since the film sneaks you toward it so beautifully and subtly that you’re left guessing right up to the very end. Depending on your perspective, the last scene is either harrowing or hysterically funny; I’ve always found it a little of both, and the horror of Rosemary’s last choice may take a minute to sink in. With an astonishing cast, beautiful cinematography and a wonderfully unsettling score, “Rosemary’s Baby” may or may not be horror, but it certainly rates as the best film that ever gets stocked in that section at the video store.