If you like manga that aren't too deep and have some pretty crack-ish jokes, this one might be right up your alley.
Since I prefer my manga to have much more depth, I already knew this wasn't going to be a favourite by any means the moment Sumi's father chose to use an experimental drug on his daughter by lying to her. If that sounds like something you don't mind, then don't let my negative opinions of this story bother you!
Still, I think my favourite character was Hozumi. He lived as he wanted to and made no excuses for himself. Plus he had some of the best humour shots in the story.
Male Hozumi in any of the frilly things he liked to wear as a girl was awesome.
So I'd say the overall story was very average to me. There were some things I liked, but too many things I didn't:
Dads treating their children as test subjects and not giving an ounce of real feeling for them (Mom too), most of the new characters introduced being experiments themselves, utter ridiculousness of some of the scenarios, plot moving from one holiday to another just because the mangaka can't seem to do anything beyond the shoujo 'episode' cliches (seriously? School Festival to Christmas to Valentines to Amusement Park Date? <-not bothering to check if that was the exact order but it was definitely something like it), and the thing that bothered me most... who she ended up with.
Not that there was anything wrong with Mitsuru in the beginning, but then Sumi, despite everyone else in the plot knowing, couldn't confess her own secret to him because she thought he'd hate her? If he was that type of person, he wouldn't have been the one she liked. Also, what does that say for the future of their relationship? That if she's ever embarrassed or has some major problem she won't be able to confide in him? But more than that, the mangaka had really shifted the feeling of the relationship by the end. I honestly can't remember her thinking anything of Mitsuru in the last two volumes other than 'cute'. To me, 'cute' is a younger brother she likes to be around, not a boyfriend. And of course, in stark contrast, there's Shizuka with whom she first shared a bathing suit, and went on to share secrets with, date, and confide in on no matter what she was feeling. Also, at one point, it really did seem like the mangaka was developing her character to be more attracted to Shizuka as a man than Mitsuru, the younger brother. So, it was really weak when the mangaka suddenly switched back to her ending up with Mitsuru.
Overall rated 7 because that's 'average' to me. I honestly can't hate it because there were some good things, but also because it didn't draw me in enough to care.