A correction, and some further thoughts:
The first rape occurs somewhere around 20 minutes or so in, not during the opening credits. The film opens with the main character (a novelist, IIRC) talking to her agent about wanting to spend some time “in the country” before starting work on her next book/article/whatever.
If you’re a fan of the genre, (slasher/horror movies) and can deal with the subject matter of the film, it can be worth watching. It was one of the earliest “slasher flicks” to feature a female lead, and one of the only ones with a female slasher.* It’s influence can be seen in Jamie-Lee Curtis’ character in the second, and the last Hallowe’en films, and, in a small way, in the Ripley character from the Alien franchise of films.
But again, if you can’t sit through multiple scenes of rape, you wanna give this one a wide berth. I can’t speak to the realism, but they are pretty damned brutal. You won’t like this flick at all.
*[sub]That I can recall right at the moment, anyway. There was a film released shortly after this, with a similar storyline. Rape victim hunts down and dispatches the men who raped her, but with a 45. Ms 45, or something similar, I think.[/sub]