Don't misunderstand me. I don't mind violence in the least, or realism, or the genre; I'm a big fan of it. I have a postgrad American lit degree so am familiar with "what is called American realist literature" in general and I enjoyed the book.
Civilisation vs savagery/the amorality of nature and human nature etc etc - Did you find it subtle? I found it very evocative at first, but after describing diarrhoea in a couple of different ways, do you need to find a third and a fourth? Then even things that aren't diarrhoea are described as being like "rectal oozings"; a man smells of "crotch", blood spurts, blood spurts, blood spurts, on and on. Drax felt quite 2d villain by the end. My objection isn't one of squeamishness, but an aesthetic one - the pudding was overegged, and I felt a more subtle engagement with the subject would have given it more depth. It felt very much like it was striking one note, and this actually strained the realism for me. It was a good read with some good writing, but yes it did feel like gore took the place of other, more complex, insights in the text.
Another one was The Son - terrific premise, told with vivid, startling, realism - then just became sex and scalping ad infinitum and lost all its edge. Even scalping and sex become dull if not deployed with restraint 
It just occurs to me that some modern adult fiction would do better if it didn't rest on these things quite so much and had to be more story-driven, and I'm merely acknowledging it requires a particular skill in children's writing to have to focus more centrally on story in the absence of this stuff.