First off, the title is misleading. It is no thriller.

The ideas and the premise are very original with lots of potential. It is thought-provoking, to a certain extent believable and an interesting topic that was chosen.

The acting was great in my opinion, maybe the best part of the movie along with the atmosphere and the visuals.

The big downside for me in this movie and what makes it hard to watch are simply that there are too many rules that the viewer has simply to accept. The non-existence of pain, the theories behind organ growth, sex...it is too hard to follow, to accept this kind of reality, and most importantly to relate.
I dont know what its like to feel no pain if I would've never felt pain at all - or what it is like to feel pleasure when someone does surgery on me.
I always appreciate movies about outlaws, feeling alienated or the classic discussion how far Art can go - but the deeper topics are so muddled in concepts that you have to constantly dig while watching the movie and being even introduced to more concepts or provocation. You can cut so many scenes and the movie still would have worked - and this is not meant as a compliment.

All in all, it was an interesting movie but not my kind. Not because it was gross.