I have one issue with the series, and it comes from the final episode; other than that, I think it was pretty entertaining.
This one issue deals with the "Culture Day festival" at the school--and, really, only one aspect of it all, at that.
Any time a series deals with characters who are in high school in modern Japan, there is usually going to be an episode or two dealing with the various festivals that the schools hold. Culture Day festivals, sports days, etc, etc--the Japanese go to school year round, but for two vacations, and these activities help to break the monotony.
The girls have a cafe, and the class next door also has a cafe--and for a variety of reasons a challenge is made and accepted. The girls rapidly realize that the class next door is going to flense them with their "Little Sister Cafe", so they move to set up a "day spa" instead.
Their first client is creepy teacher #1, "Idol" Odagiri--and Eriko proceeds to take care of him, and for me this was the series' big sour note. But to explain why I first must describe the "soap palace" or "soapland".
A soap palace is a place where a man can go to be bathed by a pretty girl. The pretty girl does not use a washcloth on him; she uses her body parts. For example, she'll put liquid soap on her breasts and then rub his body with her breasts. (She'll use other body parts too, of course.) It's a form of prostitution.
So when Eriko takes care of "Idol" Odagiri, she spreads lotion on his back and proceeds to rub it in with her groin and her breasts. She's wearing a one-piece swim suit, but it's still reminiscent of a soap palace. Naturally the guys who are watching immediately line up to be next.
This was a sour note for me because that seemed utterly out of character. In episode two--the health exam episode where all the girls spend the entire episode running around the school in panties and hospital gowns--at the end, Eriko must wait outside in front of the school, in this getup, to get her exam completed, and she says, "Now I can never marry!"
It's a common humor device for a girl--who has been groped or seen nude by strangers--to tearfully exclaim that now no one will marry her. (Even when the girl is worldly enough to know better.) In Kodomo no Omocha, the main character, Sana, comes home from a school trip after a boy steals a kiss from her and says, "Mother, I have been ruined at the age of 11."
For Eriko to go from that attitude to cheerfully providing "special service" to one of her teachers just isn't supported by the events of the series; not even in the context of the contest between classes. Eriko isn't a slut--none of the girls are--and that kind of action is just not the sort of thing I had come to expect from any of them.
It doesn't make me hate the series, but it's kind of disappointing.