I mean the story is by no means bad or even average. With just 11 chapters it managed to show multiple mostly complete arcs, character development, introduce new characters and flesh out the logic of "good" parasites in contrast to "bad" parasites. The artstyle was good, it showed what it needed to. Sakura's sexual jokes were disturbing but this was resolved by later chapters as firmly her way of showing family affection rather than actual romance. Sana was a great character, conflicted by her existence as a parasite. This conflict seemed similar to Kotaro's social isolation. I quite enjoyed the message, that's its okay to reach out for friendship and take risks rather than be a loner all one's life. The three best characters of the cast all had this theme.
The biggest problem is this story was too short. Each arc needed multiple chapters of slice-of-life content to flesh out the characters and get them ready for future arcs. I can easily see this having had six or seven volumes, a shame it didn't.
7/10.