Way before Zack Snyder "ruined" the DC heroes, he helmed the film adaptation of 2009's Watchmen. It was the early days of the current superhero hype and while the film was decent, there was no sequel because...there was really only one graphic novel anyway. So what's this new trailer about then?
It looks a lot like vigilante action and hero-distrust are going to fuel the plot, which isn't exactly a sequel but takes place in the world post-Dr. Manhattan and giant squid/exploding nuclear plants. We like the suggestion that Rorschach's journal got out and led to the creation of these masked groups. It'll make some good cosplay, that's for sure.
The show is also headed by Damon Lindelof of Lost, which seems like a good fit for the plot—because we don't expect anything less than a convoluted, fun time from Watchmen. The show premieres 2019!