Okay late to the party but here are my thoughts!
Ending Analysis:
So the gentian flower in the final chap title symbolizes, among other things, deep love and victory, so you could say it hints at both characters actually finding the love they wanted, even if both cases are delusions.
Mikoto dies imagining Makoto enthusiastically indulging in her kink, and Makoto will live the rest of his life pretending Mikoto only felt disgust towards him.
Series Cons:
Like lots have said, there was a lot under-explored, but one thing I was very disappointed to see lack payoff was the motherhood/rebirth theme that seemed to permeate the series; even one of the last chaps refers to pregnancy! The frequent sexuality_associated womb imagery and Makoto mentioning a few times that he saw Mikoto in a motherly way just went nowhere.
Mikoto's burgeoning understanding of Makoto's past, circumstances and motivations also came to a grinding halt in favor of fetish-of-the-week filler chapters unfortunately.
I also think Shuichi's arc didn't get implemented as effectively as it should have. He just popped out of nowhere to do stabbities and disappeared! With him having several dedicated chapters leading up to his murder attempt, I expected a lot more. His brother literally had no place anywhere!
Mutsumi also needed some exploration. I liked that he and his actions towards Makoto were kept vague, but imo his motivations needed more clarification.
Pros:
Honestly I LOVED this series. It has its issues, but it does so much right. The composition and art is expressive and visceral; there were lots of pages that took my breath away, usually in disgusted horror lol. The contrast of subject matter and presentation made it easier to see into the characters heads, as they would likely not see the gravity of their actions and situations. It made the whole story both easier and harder to stomach!
The characters are all but impossible to root for, unless you're like me and actually veiw them with a lot of compassion. After all, the highly detailed anotomical representations of character's paraphilic arousal is a glaring reminder that people cannot choose if something arouses them. It's mostly a tragic story if viewed that way.
Lastly, I want to say this is absolutely a niche appeal series and needs a massive trigger warning for anyone who has history with abuse. I don't agree but it could easily be argued that the series treats that subject disrespectfully.