This is an incredibly messed up manga.
It's also a really fucking incredible manga, period.
Every character in this story has a story of their own. The main characters and the supporting cast have something that really makes the reader hooked onto them. Compared to other stories, the author really takes their time with carefully weaving together a string for every single one of them, and then intertwines said strings to create... I don't want to say "masterpiece", it's hard to find a word, really. The characters are all realistic as hell - not realistic as in things they do happen often very often, but realistic as in based on what happened in their past, you can clearly see the justification in what they are doing - no matter how disgusting or foul it may be.
It's dangerous to really take the story to heart though. Although it is very well written, I cannot say that there is even the smallest amount of what one would call "the moral of the story". In the end no one should ever try to experience anything that goes on in this manga.
If there is one thing that this manga is, it's emotional - not your usually break down crying or sunshine and rainbows kind of emotional, but instead emotional with much darker, almost melancholic tone. I don't want to speak for everyone, but I personally could relate to the scenarios taking place in a way I have never experienced in any kind of story. Every action made by someone is something I can imagine myself doing if I were in their situation
I can clearly see why many people wouldn't enjoy this story, as it does cover some very heavy topics, but if you are willing to take the plunge there's no real harm in doing so. Who knows, maybe you'll enjoy it, maybe you'll despise it. Either way, I highly recommend at least giving it some time to take a look.
As for the art, it's flawless. 10/10. No arguments will and can be made against this. I can count the number of manga that have comparable art to "Shounen no Abyss" on a single hand. The artist masterfully adds a whole other level of emotion with the way they depict the characters in their art.
All in all, it's a beautiful story. The way one may interpret it as beautiful may vary tremendously compared to the way others do, but it is inarguably, incontestably beautiful.
Thank you for your time.