What makes a good sequel?
As I've just started the third book of the Captain Smith series by Toby Frost I started to think about what makes a good sequel. I pondered over books, films and music and come to an unsurprising conclusion: something new.
For example, Men In Black was a very successful film and spawned a far less successful sequel. It wasn't that the second wasn't funny (it was), but that we didn't discover anything really new about the situation or the characters. For me it was very much a case of 'I know what's coming'.
With the Harry Potter books, there was always something new in each book, especially with the revelations about Severus Snape. With Toby Frost's second book, he showed another side of Suruk's family that came as a surprise, but without being unrealistic.
In music, bands and soloists almost have to recreate themselves with each album in order to keep the interest of people outside of their fanbase, something that the late Michael Jackson and bands like Queen managed to do well.
So the key to keeping a series going is to have something new each time. Something unexpected, but believable.