The original comic New Frontier was a lavish, loving tribute to both the heroes of DC comics and the spirit of 1950s America, and this movie captured both almost as well. Many of the comments here that are critical of this film apparently are not at all familiar with comics of that era, and don't realize what this story tries to evoke. Some of the incongruities (Batman and Superman's costumes, the white Green Lantern) are NOT errors or sloppiness. These were depictions of the characters as they were nearly a half century ago. Remember, there were visions and versions of these heroes that existed prior to the Cartoon Network, and this is their story.
I love the Justice League cartoon, and this movies stands shoulder to shoulder with the best of that show.