I give An Unkindness of Ghosts a clear 5 stars for characters, worldbuilding, and social commentary. I would go with 4 stars for plotting and pacing. Though it certainly doesn't lack for excitement and intrigue, it reads a bit episodically, with an underlying emphasis on each episode illustrating an experience more than carefully crafting a narrative. But what they illustrate is powerful and significant.
"This isn't about how I feel, officer, and this isn't a personal matter. It's a Matildan matter. Our social order depends on our ethical order, and our ethical order depends on acknowledging and rectifying moral wrongs. So yes, an apology would be appreciated, but not for my benefit, but the benefit of the society in which we all live."
Matilda is a huge interstellar vessel that has been voyaging for generations--over 300 years. The society of survivors it ferries relies on a rigid social order maintained by strict adherence to rules. And it's a familiar order: lighter skin with all of the wealth and privilege in the upper decks descending to darker skin and more menial labor below. The decks have been so divided that over the years they have each developed their own dialects and languages and subcultures. Access to location, food, medicine, and knowledge is carefully controlled by guards who are free to beat and abuse anyone they like. Everyone's identities and roles are narrowly defined.
[Aster] agreed that she wasn't special, not in the colloquial sense that implied one's difference was praiseworthy. Rather, she was plain-old strange. Always had been.
Aster has never fit any of the definitions. She is an orphan from the lower decks with a personal connection to someone with the highest privilege. She has a brilliant mind even though she is not allowed education. She has never had a servile moment in her life. She doesn't meet standard definitions of beauty. Or sexual orientation. Or gender. And she doesn't relate to language, feelings, and interpersonal interactions the ways others do.
"You're a little off, aren't you?" The woman grabbed Aster's chin, turning her face so they were forced eye to eye. "You're one of those who has to tune the world out and focus on one thing at a time. We have a word for that down here, women like you. Insiwa. Inside one. It means you live inside your head and to step out of it hurts like a caning."
Aster just wants to be herself, but her world cannot allow that. Her very existence undermines the social order. So the more Aster tries to pursue her interests and talents, the more she risks mockery, imprisonment, beatings, rapings, and worse. Her passions include medicine--providing care to the lower decks that might otherwise be denied--and solving the puzzle of her long-dead mother, an astrophysicist mechanic who might just have discovered lost secrets about Matilda that could change everything. She pursues them with the help of her loved ones, her Aint Melusine, best friend Giselle, mentor and fellow misfit Surgeon General Theo, and a complex web of others throughout the giant ship.
Aster's story is just as layered and complex as she is. Just as real and personal and nuanced. As eloquent, expressive, and heartfelt. And, though often painful and not exactly enjoyable, important and rewarding.