Martyrs is definitely a game of two halves. In the first half two past victims of abuse turn up at their abusers' house to exact revenge. There's lots of shooting, violence, dirt and blood, all filmed in a single house, giving the whole film a sense of cheap convenience. None of the first half is particularly enjoyable.
I'd stop the film bang on the half way point and take some half time refreshment as this will be the most enjoyable part of the film for you. Have a cup of Bovril, a cereal bar, a balti-pie, read the back of the DVD and brace yourself for the second half.
The second half is particularly uncomfortable viewing with plenty of torture, abuse, hair cutting and degradation. The main problem is that all this nastiness goes on and on and on. Until we finally get to the plot, which surprisingly helps you to make sense of all the unpleasantness, but not in an especially good way.
After watching this and Frontiers, I've got to say I've got significant concerns about France. The only positives are that none of the actors look like they're acting and the 'cheapness' factor tended to disappear in the second half. I can't wait for the Hollywood remake that is apparently on the agenda!
If you like this you could also try:
Frontiers, Switchblade Romance, Inside.