I was not impressed. I liked the tone of the novel, I felt like James did a good job with Austen's language. However, I was struck a bunch by anachronisms.
First, I relatively recently read The Poisoner's Handbook in which Blum describes the development of police techniques and forensic in the early 1900s in America. I'm assuming that Blum's nonfiction book was more accurate that James' fictional account and am going to take that to mean that the comments about things like leaving evidence in the woods where it was found so that the police could identify it as a murder weapon and being concerned about the size and orientation for the blow and the use of post morteum examinations WOULD NOT HAVE HAPPENED.
Second, they were excited about the new fangled water closet, which seems a bit out of reach. Per About.com, indoor plumbing was not really available until the mid 1800s (and this takes place in 1803).
I did like that James was able to use the backhanded comment about truth being more far fetched than fiction while simultaneously evoking Pride and Prejudice: "if this were fiction, could eve the most brilliant novelist contrive to make credible so short a period in which pride had been subdued and prejudice overcome?"
Overall it was mildly entertaining but not very compelling. As far as a murder mystery it wasn't very good but it wasn't bad as a period piece with regards to the language.