I have loved and felt so-so about Gail Carriger's Parasol Protectorate series books and unfortunately Etiquette & Espionage falls into the latter category. While the book was not poorly written it was simply not engrossing.
Sophronia is a decent character, similar in a way to the Parasol Protectorate's main character in a number of ways. She is adventurous, pushes societal boundaries and she also has a bit of humor. However, her age being fourteen felt as if it limited what could be done with the series, or at least this particular book. The finishing school being a finishing/espionage school combo was intriguing, but it did feel a bit stale after awhile. The school and other aspects did start to become a bit repetitive, such as Sophronia kept mentioning her growing criticism towards clothing etc. that she would have had no problem with prior.
The first half or so of the book was entertaining and I enjoyed getting to know the characters. However, I did feel as though the plot progressed very little or at least very slowly and the situations grew a bit stale. I did like the connections included to the Parasol Protectorate series, including characters you get to see as children.
Overall Etiquette & Espionage is a decent book, but not terribly engrossing.