I can't put five stars on this because I did not like a certain aspect of the ending.

After some deliberation and consideration I will say, that this book, is in fact a good horror book.
That immediately means that it's not for everyone, and I would even say it's not for most people.
There's a list of topics it deals with but it can be summed up by just saying it's about child abuse, simple as that.
My first thought when reading the book, as I like to go in as blindly as possible, was that this was just another case of "let's idealize and normalize behaviors that aren't and were never cool as a background for my horror book" but I was in fact, mistaken.
Because I believe the book starts in that premise to lure you in, to start as "one of those books" and then make you realize that it's precisely about that normalization of violence against children that's so prevalent in the 50s and 60s.
The author goes on to say that this was normal and feeling powerless, feeling like you belonged to whatever adult took care of you, was a normal and regular thing.
"Children got beat" he said, as if it was a matter of fact and not the horrible thing that should never happen, but not because he the author believes it so, but because when you're a child in that situation, you are raised to believe it is an inevitable fact of life, precisely because everyone around you also went through it. My own father lived through it and I can tell you, he was a severely hurt man.
So kids are raised through abuse, to accept abuse, to then become abusive when their time in power comes, ad infinitum. It's about that horror cycle that we, generation after generation, are trying to break. And also it's about looking square in the face to those who're like "back in my days we had true childhoods and we got to experience freedom and innocence". Like, my sibling in sin, you were beat up, smoked and drank at age 12 and your parents had to have an ad on tv to remember to check if their children were home at night, do not lie to me.
Also 
If someone reads this book and stops taking the book seriously after "descriptions of underage breasts", then they're not reading critically, nor thinking critically in my opinion.
Because it is precisely about that, about how boys are turned to evil and perversion by action (and inaction) of adults.
It's not gratuitous, it's for a purpose, and just because it exists in the narrative doesn't mean it's pornographic for the same reason that any bodily description is not inherently pornographic
hell, erotic scenes aren't *inherently* pornographic either, it depends on execution and context as everything in literature. And even if it was gratuitous, that gratuitousness does say something. It's a horror book, it's supposed to cause feelings of dread and make you uncomfortable, and this book does it so well. 
I'm glad I've read it.