It was surprisingly nice.
The art is good, but nothing extraordinary. Story is much better - typical for manga in some ways (the matter with the Kiriyuus), but still something original.
Firstly I believed that it'll be another incest between father and daughter (OK, he's step-father, but still I don't like it - even if he's young, he's still her father).
Fortunately - there are some quite incestuous fragments, but's it's not romance. Hooray!
The heroine, Mei, is quite normal and nice girl. Her step-father's personality makes him interesting character, but honestly - it's oneshot. And it's fair as the oneshot, but whole story lacked something. I liked
that it was about parent-child relationship without any romance, but it's not enough to became good manga.
"A small world" has some strong points - topic and main hero (Reiji) - but that's all. It's too average to be remembered for long.