One of the big concerns that has been brought up elsewhere and at times here about a JL movie is that DC would be entering it without the build-up that Marvel had, and what little build-up that has happened and will happen has been messed up (Green Lantern) or has plenty of concerns surrounding it (Man of Steel). But all of this kind of gets me: we're forgetting a few things: 1) Unlike every Avenger except the Hulk, the Justice League has been in the broader popular culture for years. Indeed one of the most impressive and welcome pieces of Marvel's movies is that they've elevated Iron Man, Captain America and Thor into the public eye more than they ever have been. But most of the Justice League has always been there, to a certain extent. Every single one of the big seven has had at least one live-action adaptation or appearance either on the big screen or on TV, and all of them have been in plenty of cartoons. In many cases, they've seeped into popular culture to the point where even if somebody didn't see any of those movies or TV shows, there would still be a reasonably good chance, for example, that they'd know that the Flash is really fast and that Green Lantern has a magic ring. 2) A good story should be able to show, not tell. If this is done well enough, you can set up an entire universe with little to no pre-established continuity. Take the original Star Wars. While Lucas did have some sort of backstory drawn up (although how big or small that backstory was is up for debate), it was, in essence, a completely new thing, with a pretty large cast and a vast universe, where we only learned what was needed to enjoy the story. The characters were in essence archtypes, people we'd seen before who we got an idea of after only a few minutes of screen time. Justice League can work the same way, if done right.