This was a fun book, but I went into it with high expectations and it never matched them. I’ve read a lot of really good, fun regency romance adventures, with and without magic, and this one feels like what it is: a fan of that genre wrote his own take for fun, but without really going all out.
Regency romance is fun genre over all, with complex manners and dresses and marriage missions, and Georgette Heyer is the clear founder and leader of the genre. Her characters are quirky and her plots of romance and manners are complex, and it all defines a time and culture of arbitrary rules that make so little external sense and yet have perfect internal structure. Garth Nix is clearly a fan, but his characters are a too flat and caricatured while the rules of society don’t have the same clarity and internal consistency.
For regency romance with magic, Patricia Wrede and Caroline Stevermer with their Sorcery & Cecilia series or Patricia Wrede alone with her Mairelon series have brilliantly added layers of magical realism to the rules of society and it all really works well. Despite how amazing the world building was in Nix’s Old Kingdom series (a series I definitely recommend), the rules of magic in Newt’s Emerald are mostly vague and hand-wavy while occasionally contradictory.
The book that Newt’s Emerald was trying to be would have been awesome. Unfortunately, it just never quite developed enough–not the characters, the plot, or the world. None of this means that the book is terrible. It just… wasn’t great.