This is because the entire series has yet to come out in English. I had to wait for 21 for several weeks, and 22 won't be out until March.
(There are !26! in all. I will be waiting quite a bit.)
Our orphaned teenaged heroine, Tohru, is living in a tent when the people whose land she's living on discover it and insist on having her stay in the house. While there, she learns they are under a curse: if they are hugged or hug a member of the opposite sex, they turn into an animal. Thirteen members of the family are thus accursed -- one for each member of the Chinese Zodiac, and the cat. (It tells the legends for why.) And at this particular house, the Dog, the Rat, and the Cat all live. Although they can erase memories, they let her stay and remember.
Which leads to a great many plots. Their lives and all the lively subplots that going to school can yield. The somewhat -- interesting family dynamics. Enlivened by the curse in the Sohma family, but then, Tohru's family is somewhat interesting all by itself. And then there's learning about the curse and who has it and what its effects are.
Tohru is bright, cheerful, generous, always thinking of others. Overwhelmingly. In part this is a reaction of the traumas of her life, a way to cope. It does seriously enliven the lives of those around her, because if you actually want to help her, you have to figure out how to help her out without input from her. Indeed, her two best friends corner the Sohmas to tell them that they are thoroughly ashamed that they didn't figure out that Tohru was living in a tent (she had told her grandfather she could stay with friends while the house was renovated, but she didn't want to impose), and they want the Sohmas to treat her well. And one character deliberately doesn't tell her something because otherwise she would fuss.
And all the other characters, in the families, in the school, are lively and a broad palette of types.
The art is something else. It's amazing how many emotions you can convey with stylized drawings. Some of them, if you are not familiar with manga, you have to pick up through repetition, because they are icongraphical, but some of it just explains itself.
I am particularly fond of the play of Cinderella they put on. The characters are woefully miscast -- Tohru as the wicked stepsister? she reads her own lines and starts crying! -- so they rewrite the play and give us Sorta Cinderella with all the characters having roles that they can play.