To a certain extent hitting on to a winner first time out isn't always the most impressive thing, the real art is in doing it again. The specific indicators of success in a sequel, after all, are more complex than an original: you not only have to make a fundamentally great film, but you also have to outdo everything the original did.
There's an unwritten rule that the threat has to be bigger, the spectacle more spectacular and the defining characteristics of the characters more pronounced. It's like the ideal is offering an undiluted, beefed up remake, with enough new material to make it all feel fresh. In short, it shouldn't be all that hard once you've done it well once.
Sadly, Hollywood - and comic book movie makers in particular - tend to get these things wrong a worrying amount. There are more disappointing superhero sequels than there really ought to be in the single defining genre of the last decade or so, and it's a wonder so many franchises even survived.
But which are the very worst? Which do the studios probably wish they never bothered spunking their money on?