It's got some pretty good actors but....
.... Pacing, man, pacing!!!!!!
It could be a dark movie, it could be torture porn, and it was well acted, but it is so freaking slow that by the time anything actually happens, by the time the story gets moving, you already don't care.
What they needed was to actually have an event somewhere in the first 10 pages of script to hook the audience, and, preferably, one that has something to do with the plot.