It's fascinating. It's a cool, creepy story, but it's also got some of the most stylish imagery I've seen in years... and sometimes the imagery is also the storytelling, all by itself. Those brainwashed squiggle eyes, for instance. Brrrr. You see those and the show doesn't need to say a word.
It's set in a house of black aristocrats ("Shadows") and their white servants ("Living Dolls", believed not to be human). "Black" doesn't mean ethnicity, though. They're silhouette-people. Their clothes are normal-coloured, but the Shadows devour all light. They can't even see their own faces... so every Shadow has a doll (or "Face") whose most important job is to follow the Shadow around and make all the facial expressions that their master can't. The best Faces are terrifyingly good at this, moving in synch so perfectly that it's as if the Shadow was their literal shadow.
Also, negative emotions make the Shadows emit soot. Great clouds of it, or sprays, or in patterns. You can identify a Shadow by its unique soot emissions... but if you don't sweep it away, this soot can become hostile magic creatures. Some Shadows even have soot superpowers, letting them (for instance) turn it into a bird to fly off and deliver a message.
Even had the storyline been garbage (and it's not), this would have been cool. It's a compelling world to visit. You could impose a thousand different readings, each valid. Racial metaphor? A reinvention of Hans Christian Andersen's literary fairy tale "The Shadow"? A borrowing from Barrie's use of shadows in Peter Pan? A bunch of horror references? Yeah, sure. Any and all of those.
Personally, it feels to me as if someone discovered Jan Pienkowski's children's books (not Meg, Mog and Owl but that silhouette style he invented) and decided to play with it. Even this show's Victorian gothic setting reminds me of him, e.g. his illustrated fairy tales from Eastern Europe and Russia.
Apparently the anime has taken some liberties with the manga. Fair enough. They're different media. I've only experienced the anime (so far) and I thought it was great. Also sinister. It starts out relatively innocuous, but gradually gets creepier and creepier as we get deeper into it. There's a sadist who's disappointed that more Debutantes didn't get eliminated, for instance. Our main characters are Emiliko (adorable and indestructibly positive) and her Shadow, Kate (apparently cool and stand-offish, but a stalwart ally of Emiliko), but all the Shadows and Living Dolls are distinctive and important.
It's fairylike, fascinating and scary. You should definitely try at least one episode. There's a second season and I watched it back-to-back with this.