Have just been reading Death Comes to Pemberley. Of course I'm a fan of Jane Austen, and likewise PD James, but the problem with this book is that the two writers are polar opposites. The essence of Austen, if I could be so bold, is character and interaction and feeling. The essence of PD is the unravelling of motivation and the gradual exposition of dark forces. Never the twain.
The result is a dead book, which just isn't interesting either as a take on Jane Austen or a murder mystery. And this is more to do with the absolutely precious and unassailable nature of a fine author's voice - I'm talking about Austen and PD James here - than with anything else. It's that elusive thing that all writers talk about - finding a voice. What does it mean? It means finding the medium through which my stories can be told - and finding the stories that match my medium and my voice. It means a perfect blend of character, plot, and narrative style. It's a struggle, it's elusive, and when it works, it's wonderful. I defy anyone to produce a really good sequel to Austen. How could you, if you weren't Austen? And why would you want to?
Be yourself. Write, yourself.