Preface I will try to keep this review completely spoiler-free not only so I don't ruin it for the poor souls who actually decide to read this terrible manga, but also for the sake of not making myself have to read parts of it again to search for examples.

Boy's Abyss obviously features a lot of dark and edgy topics for better or for worse. Be careful if themes centered around depravity affect you in negative ways.

Story

Boy's Abyss can simply be described as a mess. From the get-go, the manga establishes a pretty obvious theme: There is a boy who lives in a town where toxic relationships between his family and peers keep him from leaving. On its own, there is nothing wrong with this concept and I think it actually has a lot of potential. Unfortunately, one of the critical things about this manga is that it cannot decide on a thematic direction and depicts the darker aspects of humanity with no real intention.

The characters go through a lot of different phases throughout the story that don't really seem to flow into each other whatsoever. For instance, it would be similar to if a biography of Bobby Fischer demonstrated his struggle with breaking into the world of Grandmasters and before ever resolving that period of his life, immediately started on his fall into antisemitic ideals. These phases that the characters go through seem as though they will be narratives on a specific subject whether it be manipulation, eating disorders, unrequited love, etc. but the narrative never comes to fruition and instead just decides to switch to the next bit of story adding to the characters struggles with no real regard for what they have already experienced. This leads the characters and story to just feel extremely convoluted and simply not make any real sense as nothing happens for a reason, it just happens because it can.

Art
As others have stated the art in Boy's Abyss is about its only redeeming factor. It truly is art in a purer form than the average weekly romcom fluff and demonstrates skill and craftsmanship that even more serious manga don't really reach. However, it obviously is held back by the fact that the impactful and beautiful shots will be accompanied by some pretty edgy lines that circle back to the core problem of completely arbitrary characterization and themes. To me, this genuinely had an effect on how I viewed the art as it just felt clunky and didn't really hold the full impact that you would expect the shots to have.

Conclusion
Overall, I'd say that Boy's Abyss is not worth reading unless you are especially into depictions of pure depravity just for the sake of it (looking at you rent-a-girlfriend readers). The manga faces a lot of issues that will leave it feeling a lot like how Kurt Cobain describes his lyrics: "I was just using pieces of poetry and just garbage — you know, just stuff that just would spew out of me at the time,"

In essence, that is what Boy's Abyss is, a shallow presentation of the darker, problems that afflict humanity with no real message or meaning behind it all. Whether that appeals to you or not should be a decision based on your own preferences, but humans tend to search for the meaning in things for a reason. The message behind a work of art is very often, more important, touching, and fulfilling than the aesthetics, craftsmanship, or accuracy of the work itself, which is why I'd say that Boy's Abyss is just not a good manga.