I read this because I had run out of Cat Sebastian books, so I might have gone into it with unreasonably high expectations, since she's one of my favourite authors. The Gentleman's Book of Vices was a fun story but it could have been a bit better. I had a good time but didn't give me the deep understanding of the characters and that prevented me from being fully invested in their romance. One thing I liked was the side characters - they were strong for the time they spent on-page and did a lot towards making the story feel more populated. Romances, even those by experienced authors, can fall into the trap of shallow and boring side characters, so that was a pleasant surprise.