One thought sums up this movie: Meh.
It's so mediocre, in fact, that I'm writing this review during the final act of the movie.
Russell Crowe delivers an intense (though single-noted) performance as the film's antagonist. The problems lie with the writing, and his supporting cast. The female lead's acting was subpar at best. Nothing about her portrayal carried the weight of the frenetic, horrifying situation in which her character finds herself.
The pace of the action is as frenzied as you'd imagine...the deaths as gruesome. For a story that has little (if any) backstory, the gravity of the leads is all the more important. The female "protagonist" is utterly forgettable, and drags down this attempt at a guilty pleasure thriller.
If you're bored and come across it, it's a decent one-time watch...otherwise, skip it.