The least known avengers(Black widow and Hawkeye) didn't even get their own movies.
Black Widow got Iron Man 2, which was really all just set up for SHIELD's involvement and setting up the characters for Avengers. Plus you got enough of her character in IM2, but by Avengers you knew really you needed to about the character so by the end you've established enough of her character and history that's equivalence to a movie.
MOST of the general public only know of Superman and Batman, and to a degree Wonder Woman.
MOST people have heard about Flash.
When Green Lantern came out, not a lot of the general public even knew what he was, and often confused him for Green Hornet.
WB/DC will have to make a film worthwhile introducing these characters still rather than banking on a JLA cartoon from 10 years ago.
All I'll say is Geoff Johns constant re-writing ruined the GL movie, I hope he's not involved in as he was in the now proposed JLA movie.
Most people only know of Wonder Woman only through the fetishistic eyes of that costume.
Plus Green Lantern AND Green Hornet had the misfortune of being released around the same time to one another. That and the general consensus being that GL was ass and no one didn't care to go see it didn't help.
Though what really bothers me is Marvel did play it right with how they did the lead up movies. Since even if you didn't see one or two of the tie in films, you could at least feel secure enough in going to see the movie because you know of one of the characters from a prior film. It kinda gave a non comic reading audiences a life preserver with following a specific character to help shepherd them to see the movie. With Justice League's plan of BIG movie first THEN establishing franchises it just seems so goddamn risky because if the movie bombs or the character fails to resonate with the audience then how in the hell is that going to encourage audiences to see that one character's film? Plus doing this so soon after Nolan's Batman universe worries me because that Batman can't coexist in a world of super powers and audiences will be linking that version to this one no matter the actor.