There's a particular kind of enjoyment that is to be had when reading a Georgette Heyer novel. The tone of each of her meticulously researched romances, set in Regency England, is consistent, charming and utterly compelling (though problematic^[1]).

The Regency world created by Georgette Heyer is the foundation of most historical romance novels set in that period, yet few come close to creating the feeling reading a Georgette Heyer novel does^[2]. Below are a few books I believe manage to do so.

Newt's Emerald by Garth Nix

Newt's Emerald is probably the closest a book has come to the Georgette Heyer feeling for me. Add a sprinkle of magic and adventure and this is an instant favourite.
Newt's Emerald tells the story of Lady Truthful, a young lady who must set off to recover a family heirloom, the Newington Emerald she is set to inherit at 18, along with the magic it bestows. What follows is a fabulous adventure, an unexpected romance, and a hint of potential future stories.

Cecelia and Kate series by Patricia Wrede and Caroline Stevermer

Cecelia and Kate include Sorcery and Cecelia, The Grand Tour and The Mislaid Magician. This series is set in a magical version of the Regency Era. Each epistolary story is charming in its own right, starting with Sorcery and Cecelia; or The Enchanted Chocolate Pot, in which two cousins, Cecelia and Kate, exchange letters, as one heads to London for a Season while the other remains at her country estate. Both experience seemingly unrelated incidents that become increasingly dangerous, face the appearance of mysterious, and possibly untrustworthy, young men and must help each other uncover what on earth is going on.

Lady Helen and the Dark Days Club by Alison Goodman

Lady Helen and the Dark Days Club is the first book in the Lady Helen trilogy. It's a little different in tone from Georgette Heyer, but Goodman's meticulous research and engrossing writing created as believable Regency world as any Heyer novel.
The focus of Lady Helen's world is preparing to make her presentation when she discovers one of the housemaids has disappeared. She is rapidly drawn into a world that is far removed from the one she is expected to inhabit. Demons, supernatural fighters, and an uncertainty of her family's past, all upturn Lady Helen's life as she must make a difficult choice about her future.