Avengers worked because of Whedon and RDJ. Not to mention the five movies that proceeded it that gave it a great lead in. It also helps that Marvel's characters are a lot more flashy and exciting than DC's characters which are more iconic. There's a reason why Captain America just looked boring next to Iron Man and the Hulk. The Justice Leage will be an entire movie of Captain Americas, and it'll be horrible.
Also the JL cartoon series worked so well because Batman was the goddamned Batman, and the cartoon gave him plenty of space to just be a badass. Good luck translating that into a 2 hour film.
Also the JL cartoon series worked so well because Batman was the goddamned Batman, and the cartoon gave him plenty of space to just be a badass. Good luck translating that into a 2 hour film.