First off, this is a very formulaic set up. That is not a bad thing, when I want an action movie, I want the action movie formula; when I want a horror movie, I want the horror movie formula. Black Rock follows the horror/survival/thriller genre of movie to the tee. Fine.
There are skinny unarmed women, who meet ex military armed soldiers and without giving away any 'twist', things get bloody quickly. The characters are roughly sketched with some solid acting, but we never really get to know or care about the characters. No problem, not what we are here for.
Where the movie falls apart is two fold: First, the best part about the movie should the Black Rock Island, a small (how small?) island with waters too cold to swim in. It is a great idea for a terrifying setting. However, it is rarely used to any effect. What makes the setting worse is the characters can both hid for a day, yet be almost on top of each other at the same time. At points the island seems to be miles long covered with dense forest, and at other points characters are hoping from one side to the other in a couple steps. This is confusing and a missed opportunity.
Second, when good horror/thriller movies set up the conflict, it almost always the strong terrorizing the weak, but the weak figure out some trick to save themselves. We as the audience need to believe that they can succeed, or be able to imagine that we could come up with a plan to survive. Unfortunately, this movie puts Labron James and (pre ankle) Kobe Bryant in a 2 on 2 basketball game with two 12 year old girls in wheel chairs. We as an audience need to believe our two heroines in wheel chairs have a chance, but we can't. The odds are so stacked against them that if they lose we are bored and if they win it is unbelievable. That is true of this movie as well. We are bored seeing boots crush ants and roll our eyes and almost laugh when that tears the booted leg off at the knee.
A long analogy, but the problem is that it is only through total incompetence and baffunery of the antagonists that the heroes don't just die 20 minutes into the movie.
Once you get past these two rather large disappointments there are other hard to overcome plot holes, like the sniper who can take out a moving target in the dark from atop a cliff with a head shot one minute then barley knows which end of his gun the bullets come out of the rest of the movie.
There is also a rather odd nude scene part way through that neither makes sense logically or in the story. The point of this still escapes me, but it was at least the only interesting character progression of the film.
All in all, it is a laboured film. It is too bad, because I looked forward to this film and was excited about the premise. The parts are there, but so much more could have been done with it. Characters flushed out, plot holes filled, more time taken with the mood and setting. Unfortunately, this Black Rock should sit in the bottom of the lake where no one can find it.