BLACK ROCK starts out with a stab at irony: in an attempt to get two friends who are no longer on speaking terms with each other to come along on a camping trip on an island, a woman pretends that she has only a short while to live. Even though she admits right away that this is a lie, her manipulation does the trick, and she gets them to come along, not realizing that she may have not been so off the mark, either for herself or her two companions.
I appreciate dark humor in movies, but when the humor relies on sociopathic behavior, it usually falls flat. In this respect, it reminded me curiously of REVENGE FOR JOLLY (2013), which was clearly meant as a dark comedy, but utterly failed as such because the main character's psychopathic behavior was so unrelatable.
Anyway, there is no obvious attempt at humor in the rest of the film, but we find that her two friends also have flaws. In story-telling, flaws can serve to flesh out characters as real humans, but if used carelessly, they can also make characters unintentionally unlikable, which seems to be what happened here.
This is too bad, because once the plot turns into a MOST DANGEROUS GAME (1932) type story, we can muster little sympathy for the hunted.
The other big problem with the script is that it strains credulity, from the drastic change in the characters, both of the heroes and villains, over the course of the story, to the outcome of a fight of survival of some very girly girls against trained soldiers.
Together, these rob the movie of audience involvement. Perhaps the most remarkable thing about this exploitation fare is that it was directed by woman, in fact the protagonist.