It's pretty interesting, I wouldn't say it's deep but it did get confusing as the story went on (in terms of relations). It has a huge shoujo cliche (it may have started it) of "we-thought-we-were-related-and-love-each-other-but-guess-what?-we're-not!!" The only really creepy part of this manga was her younger brother, which is why I'm leaning onto the negative side of this. The fact that he does the stuff he does even after knowing Yuri and Sumire are his siblings makes him really freaky to me. Also the whole "imitate my brother's dead fiancee's haircut" was just the crazy cherry on top.
As a character, Yuri actually isn't that bad. A little over-dramatic, sure, but it's shoujo. She's also pre-occupied with her self-image, but again, considering the circumstances, I would probably be self-conscious, too, if people told me everyday I was fat and ugly. You can see she brushes it off as the series goes on and doesn't let "you're fat" comments get to her anymore. The older sister is also a character I really enjoy: she cool, tough, and she doesn't mercilessly pick on Yuri, but rather helps her. Sumire is really a tragically cute character overall. Also, his over-concerned ways are really humorous!
However, the younger brother's incestuous feelings really, really ruins my experience with this manga.
(* Someone was wondering why this is josei but won as shoujo award is because they have overlapping demographics. I also would classify this as shoujo because even though Petit Comic is a "josei" magazine, the manga they serialize are more or less shoujo with more adult-themes not suited for the entire range meant for shoujo, which is thirteen to eighteen-ish)