It's one joke repeated every chapter; but it's a good enough joke. One of the few manga I'd probably recommend everybody to check out but nobody to finish.
I'm surprised how the author manages to make such a concept not get stale.
Also the friendship between the Doll girl and that one schoolgirl is pretty wholesome.
Looks like this is why a good plot makes bad art in manga seems irrelevant. Jokes is good, story is good, definitely better than most of webcomics out there with a good art but crap plot.