I've finished the book and on the whole I thought it was okay. The only thing that really bothered me was the magical/supernatural elements. I kept permanently saying to myself while reading the novel: That's so unlike Jane Austen. And IMO being like Jane Austen is what a sequel's major ambition ought to be.(It goes without saying that nobody can succeed in doing that!)
Therefore it's really annoying that the characters act so unlike they used to in P&P. Lizzy, as you've already mentioned, seems quite different now and Caroline is hardly recognizable. To explain her strange behaviour by dark magic is not satisfactory for me.
I share your disappointment, Geri-Lynn.