I read Melmoth (but have not read The Essex Serpent)
It was beautifully written but found it very disjointed and none of the characters really went anywhere, despite their early promise. There is a really good story in there somewhere, it just didn't manage to find its way out. Maybe that is the point, but I found it a disappointing read.
Not sure if I want to try the Essex Serpent.
I am a sucker for a nice cover though!