To be fair, I have not read Black Bird in its entirety. I did, however, read the first six volumes. The premise was interesting, but the characters kept me from actually enjoying it.
Misao, the protagonist, is passive to the point where it's obnoxious. There's a reason nearly every tankouban cover is a picture of her crying, while Kyou looks either pleased by this, or annoyed. Also, there are flowers. Misao has gotten slightly better over the course of the series, but not by much; she's moved up from just crying to crying while buying herself some time in a bad situation, but still being ridiculously naive, and still pretty weak-willed.
Kyou, the main romantic interest, is a jerk. He doesn't really seem to care about Misao's feelings, or the word 'no'. But he's all that's keeping her from being eaten by somebody else, and he's suuuuuper pretty, so Misao forgives him.
The other demons that want to marry Misao would happily settle for raping her.
Basically, the fact that nearly all the male characters are horribly misogynistic and that this is considered okay because they're good looking really bugs me. And it's not just other characters forgiving them, it's the tone of the story itself. The relationship between Kyou and Misao is really, really dysfunctional.
Overall: decent art, so-so story, horrible characters. I don't recommend it unless you have a fetish for good-looking guys with terrible personalities.