On the basis of regression to the mean ( http://en.wikipedia.org/wiki/Regression_toward_the_mean ), or what we might call the "J.K. Rowling effect," it would be far too much to hope that the sequel will match the original. Nonetheless, this has got to set some sort of record for the gap between a novel and its sequel. Interestingly, there is a list of gaps between film sequels ( http://en.wikipedia.org/wiki/List_of_t…
So a huge gap between publications, but I would expect the writing to be similar.