If it was written better, the smut and story could be great. I do not find the main couple appealing personally. I preferred the other two couples. Specifically, the second-born couple. They have so much potential to be a good, well-written story. I wish that this manga had longer sex scenes for each couple and not just little snippets of sex scenes about the two side couples. The smut was good, though it could be better.
Overall, I would definitely read this from time-to-time, but not because of the story, but the fact that this could've been so much better, so I just imagine another plot line for this manga in my head.