The CHARACTERS are very good. I suppose there is a balance between characters being plausible and being interesting, and they attain both. They have their own flaws and issues, quite a few severe issues, but they keep trying. You might say some of the characters cross the moral event horizon by some of their actions, but overall they are sympathetic.
Finally, the STORY, okay, well, first, a major theme in the story is that children should be allowed to be children. That taking advantage of children is monstrous. Sure, the artwork is a bit explicit at times, many times, but this point of the story should not go unmentioned. I won't spoil by divulging how or when this point comes across, but it should be obvious for anyone who has read the entire manga. So, let me reiterate that: children should be allowed to be children, and not taken advantage of, regardless of your own feelings or even if the child express affection.
I do find this point rather ironic, considering the explicit artwork.
The story, overall, has several heartwarming themes to them. The story, at times, divulge into rather dark territory, but the lessons and morals it aims to purvey are worthwhile. What it means to be a parent, what it means to be a teacher, and how those... jobs can _feel_ if you are emotionally invested. Granted, you may feel that some parts are inappropriate.
