I don't believe i've read any of P.D. James' mystery novels before now. I read Talking about Detective Fiction back in 2010. I saw Death Comes to Pemberly somewhere before Christmas and stuck it on my library hold list on a whim. I've never read any of the continuances of Jane Austen novels either
So I thought when I picked this one up that it was going to be an English country house-type mystery with Elizabeth and Darcy in the role of the detectives. This book was not at all like that. The murder takes place on Pemberly's grounds, out in the woods. Without going into spoilers, Wickham and Lydia are involved. There really isn't any detecting going on; a gentleman is accused of the murder, basically says he didn't do it and expects to be believed. There's an inquest then a trial and Darcy has to testify. I didn't even find it very suspenseful.
The redeeming quality is the James nails Austen's voice. The novel does feel like a continuation of Pride and Prejudice. Lizzie and Jane are both happy mothers of 2 and 3 healthy children, respectively. All the kids are under 5 and we only get to see the two Darcy boys. Lydia is still a scatterbrain; Mr. Bennett adores Pemberly's library. In a way it is like catching up with some old, formerly close friends. I suppose that is why there are so many Austen continuations and imitations.
I give this one a 5 overall but I would say you won't like it if you don't enjoy Austen or require your mysteries to be the main focus of the story.