First, the atmosphere of the movie is unique, even if it's not like The Exorcist. Polanski manages to create an environment of tension, isolation, and unease with simple scenes. The sense of isolation and betrayal that Rosemary feels is so intense that it makes you feel her uncertainty and terror.
Second, the film is pioneering in how it uses psychological horror. Instead of ghosts and sudden scenes, aka jump scares, the real horror comes from the feeling that you can't trust anyone—not even the people closest to you. Another example of psychological horror is the moment when Rosemary faces her baby, but we only see her reaction. Personally, I felt like I was there, and that unique kind of terror really hits you. How everyone else reacts makes it even scarier. Damn you, Polanski!
Now, as for Rosemary's character development: She starts off as an innocent and naive young woman, full of optimism for her future and family. As the film progresses, we see her transformation, both psychologically and physically. Her haircut, for example, is a significant element of this transformation. Rosemary's short hair could be said to symbolize the loss of her innocence and her attempt to regain control of her life. The theme of identity is characteristic of Polanski's films.
Then, as Rosemary begins to understand the reality around her, she becomes more determined and resilient. Despite the horrific revelations and the betrayal by those closest to her, she continues to fight for the truth and the safety of her child. This development of Rosemary makes her character multi-dimensional and very human.
Finally, the film manages to remain relevant even today, as it explores themes such as female autonomy and social pressure. Rosemary is a woman struggling to maintain control of her life in a world that constantly undermines her.
Regarding Polanski, his personal scandals are undoubtedly serious and should not be overlooked. However, his work as a director has left an indelible mark on cinema and can be appreciated separately from his personal life.