The thing that I like about Martyrs is the fact that you think you know what sort of film you're watching and then the rug gets pulled from under your feet. A couple of times. What starts off as a fairly standard, but good, revenge story, mutates into something far more disturbing and deeper by the end. The ending, in particular, provokes much thought; I've got a couple of theories, my preferred one involving eternal hell and Satan jabbing his red hot poker up evil-doers nether regions.
Everything in Martyrs suggests a director making a quality product on a relatively low budget. The make up effects are simple, yet very effective (and wince inducing). The soundtrack by 'Seppuku Paradigm' is excellent. Just as I could watch the intro screen to the Blu-ray of A Bay of Blood for hours because of the music by Stelvio Cipriani, the same applies to Martyrs. The two leads, Morjana Alaoui and Mylène Jampanoï are believable throughout and performed many of their own stunts; Alaoui actually broke three bones, in a safe non-stunty scene, which stopped them filming for a month.
Now to the controversial matter of misogyny. There are some very harsh images of a young woman being systematically beaten, force fed and humiliated. Taken out of context, you just can't defend this. But the first half of the film makes you care about the woman in question; when she is tortured you want: A) her to escape, B) her captors to suffer intensely and C) her captors to suffer intensely due to hedgehog insertion. There is no point - unlike when you cheer on Jason in every Friday the 13th - where you side with the captors and want to see what they are going to do to her next. You want it to end. Couple this with the ending and I think you have a film that explores what people will do for their beliefs and not one that celebrates violence on the female form. (Doccortex thought it was great that I was doing a review championing Martyrs because he gets to look like the sane one, and I get to look like a mentally unhinged psychopath. Thanks for that buddy.)
It isn't a film that is pleasant to watch. It has a great atmosphere but after the credits roll you will probably need a palate cleanser: Antiques Roadshow or Mrs Brown's Boys perhaps. I had to watch an episode of Bleach to return to a happier place. From reading both reviews you will know whether you even want to bother giving this a go or not. Horror fans with strong stomachs will have a stronger chance of liking it than most.
If you like this you could also try:
Frontiers, Switchblade Romance, Inside.