In a postmortem of The Leftovers, the man behind it - Damon Lindelof - explains he made a mistake when making Star Trek Into Darkness. "There's no reason to be mysterious just for mysterious' sake."

He used the Star Trek reference when discussing the audience's preference for mysteriousness. He admitted that there's no formula for what to keep secret and there's no exact timeline, reports say.

".. for example, we decided we weren't going to tell people that Benedict Cumberbatch was playing Khan." He goes on to explain that it was a mistake because eventually everybody knows he's playing Khan. 

But what irked the audience is not the fact that Cumberbatch was a hidden character. It was because they left the fans confused on the character billing. Initially, everybody was excited to learn from the first teasing trailer that Cumberbatch was going to play Gary Mitchell, a star fleet officer.

Then a trailer later, it got terribly confusing when Cumberbatch shows up as a very ominous character seeking vengeance. Vengeance for what? That twisted the fans' hair a little bit. Since Cumberbatch became a different character in between trailers, the confused fans were ouraged at the deception and felt they needed an apology. That also includes Cumberbatch himself when he admitted that he's not playing a character named John and not Khan.

Why the secrecy, Lindelof?! 

So that means there is a portion of the truth hidden from everybody but then eventually the truth was found out. Compare that with J.J Abram's Star Wars movie. Lindelof says Abrams has not spilled the beans on the movie. "... and we love it" Lindelof exclaims. He said he's never met a person who wished he knew more about the Star Wars movie. 

So there you go, film makers. Don't go twisting the confused nerves of your franchise fans. Instead, build the excitement.