I had read this book before and this time listened to it in audiobook format. This format made it a bit difficult to differentiate between the many characters earlier in the novel.
I find P.D. James to be a good writer and I really like her detective featured in her mystery books (Adam Dalgleish of Scotland Yard). I enjoyed this book in particular as it had a good plot, interesting characters, realism, and some interesting commentary around life in general and psychiatry and related disciplines in particular. The one drawback is the time period of the book is from a time period where some people still used a horse and carriage (there's cars too though ;) and that may not sit well with some readers.
James writes a more 'thinking person's mystery' with the emphasis on psychological factors rather than car chases or that kind of thing (not that there isn't that kind of material at times). Even though she writes mysteries I would describe her as a writer rather than a mystery writer.