The Glamourist Histories start with an extremely well-done Jane Austen sort of Regency romance with magic as an art form. Then with each subsequent book Kowal makes great leaps in the development of the art, development of the characters within their marriage, the opportunity to take her couple places Austen never went like the Napoleonic wars and the slave trade, while always managing to maintain the Austen tone.
It's kind of astounding even though Novik does essentially the same thing with the Forester/O'Brien tradition of naval war novels.
And now I'm off to read, because writing this up I realized that I skipped the second book in the series entirely. I knew my September was rough, but, wow, that's a pretty huge error to make.