I did enjoy the writing of this book, even though I was horrified by many of the events depicted.
I was interrupted in the reading of this book by exams. Up till then I found I was enchanted by the twin experience, in spite of the terrible setting. When I returned to the book the spell was broken and I felt I was reading about innocence twisted by evil slowly becoming despair, vengeance and then forgiveness.
Even though the twins despaired at their separation and the loss of a part of themselves, I never got the impression that they were identical in soul. This was reflected in the different trajectories of their stories.
It also made me think about where our sense of self hibernates when events do their best to crush it.
It's not for everyone and some may think "oh no, not another holocaust book". But maybe there's something in the zeitgeist that is drawing our awareness to it as a warning. I'm not sure it's 'torture porn'. There's many other more salaciously violent stories out there. And there is a case to be made for facing evil directly to keep it at bay rather than turning away from it and missing it creeping up on you before it's too late.