I remember comic fans on message boards posting that they thought Joseph Gordon-Levitt looked like Heath Ledger. Which meant that he could play the Joker. Levitt was cast in Nolan’s Inception, and that got their hopes up that he would appear in the upcoming Dark Knight Rises. And he was cast for it. Except he’ll be playing John Blake, a young police officer, who hasn’t actually appeared in the Batman comics. This wouldn’t be a first for the series, as Rachel Dawes, the romantic interest in the first two films, was also created for the films.
Because of the initial speculation that Levitt would be the Joker, some people are going to go into the film expecting a big twist. They may tell a few friends about the possibility, increasing the amount of people expecting the sequel to one of the highest grossing films of all time to include its most popular character.
So if Joseph Gordon-Levitt’s character isn’t the Joker in disguise, some people in the audience will be disappointed. Because it’s really unlikely that anything John Blake does will be as cool as the most impressive thing you can imagine the Joker doing. It’s the difference between an okay supporting character and one of the most popular screen villains ever.
Unless John Blake turns out to be the Joker in disguise. That would be fine. Due to all the speculation, some viewers will see it coming. Though I doubt any of them would be disappointed.