The first thing you must know about this is that everybody's basically named the same: Haruka, Haruki, Hikaru, Hanabusa... for real? I mixed them up so much, fuck you author-san Q.Q you did this on purpose didn't you?!
Joking apart, this manga tackles some heavy themes like rape, death, suicide and pathological relationships really well. It takes the most controversial themes from BL, the themes BL is hated (and loved) for, and makes them feel real, showing how ugly they are and how they can destroy people. The themes are portrayed seriously: people realise they're victim of sexual violence, therapists are taken into account, etc. So if you want a dark, tough manga that fully knows how bad the things it portrays are, this is it.
Now, speaking of my personal thoughts on the series, I loved how this makes you torn on who's to blame. Of course what Hikaru does is wrong, but you are brought to pity him because of his history, how mentally ill he is and how much sorrow he feels. His humanity is shown in his pain and in his love for his mother. Haruki makes you understand what being desperate really means. His slow and gradual fall to the pits of hell feels very real. The other characters are portrayed more quickly, but they look realistic as well. I'll be that person and say
that I was hoping for Hanabusa and Hikaru to get together at the end. But the manga decided to stay realistic, showing how Haruki cannot get 100% back to normality. Ever? That's left to our interpretation, as the ending is somewhat open, hinting that it will still take a long time for Hikaru and Haruki to get their mental health back, if they ever will.
As for negative points, the art is baaad. The fact this manages to still be good is admirable, but I wish characters well drawn better. The non-anatomy really killed my eyes in some scenes. As for the time skips and point of view changes, I appreciated them as they are proof of an actual attempt at narration. I say "attempt" because as someone else mentioned it was not 100% successful. Sometimes I was confused and needed some re-reading to understand what was going on. But other times I found it meaningful and nice. This felt like a proper story and not just as sequence of scenes told neutrally.