I saw Seanan McGuire at a convention. She was in full “act like a fabulous author GoH” mode, and could not stop giggling about exploding hawiian rats and the tapeworm she ate on purpose. So, she doesn’t take herself all that seriously, which is the right attitude for her books.
The world starts as the standard “every mythical creature you’ve even heard of is real”. The twist is that the secret society keeping humans safe succeeded hundreds of years ago and are now killing harmless, even useful beasties (cyptids). Our heroine is from a break-away family devoted to the study and preservation of supernatural ecology, and hunted by the now-evil monster-killing group.
The rest of the twist is inventing crazy creatures – talking mice (that’s all they do) and dragon princesses which look human, breed asexually, live in groups and single-mindedly collect gold by working regular jobs, then buying the gold.
Personality-wise, our heroine fails to be insecure or mousy — rather the opposite — but she’s got money problems and has trouble meeting guys since she works so much: protecting the harmless monsters of New York; a waitress in a non-human topless club; and a contestant on “So you think you can dance.” That feels sufficiently weird to make up for her being 100% human with no special powers. But she’s trained in ninja skills since birth to where she spider-mans (parkours) everywhere over rooftops, and her famous renegade family name is like a magic spell to make monsters cooperate.
The plot is a fine sprawl of mostly personal problems mixed in with the adventure: she has to help her telepathic non-human sister; the guy from the evil monster hunters is in town, and he is smoking hot; and humans mutated into lizard-men are using monster blood to power a world-blasting magic spell. What really puts this over as an urban fantasy female detective book is the big baddie: he turns out to be friendly. The evil lizards were worshiping him, but also keeping him sedated. A little friendly conversation, which no man would have considered, solves the crisis.
The rest of the series gives us more books with this character, but then we get more family members. There’s her roller-derby younger sister, and then her brother. He’s a non-violent researcher, clumsy around women, with strong female role models — but he’s still written as a guy, blundering through his book as a big, dumb ape, occasionally listening to his girlfriend who’s the brains of the operation.