Problem with Justice League (and the DC Universe) is they never built up to the big team movie like Marvel did. In the Avengers, Iron Man, Captain America, Thor all had their own movies (plural) before The Avengers came out and Black Widow was in Iron Man 2. Only Hulk and Hawkeye made their first appearances in The Avengers.
They built up to it, which made it an even and then built upon that with more Avengers movies and solo movies.
JLA was a mess. They saw the success of The Avengers and wanted to recreate that success. I mean they have Superman, Batman, Wonder Woman, Flash, Aquaman and Cyborg. (personally I only remember Cyborg from New Teen Titans but anyway....)
They shoehorned everyone in: Batman (last solo movie was 5 years earlier with a different Batman), Superman, Wonder Woman (just had her first solo movie only months earlier, Flash (no solo movie), Aquaman (no solo movie), Cyborg (no solo movie).
If they only waited 5 more years and produced a solo Batman movie along with Aquaman, Flash and maybe a Cyborg movie then they could have had a cohesive and exciting movie.
Looking forward to seeing the new cut though. Even though Batman is still in limbo and still no Flash or Cyborg movies (I want a New Teen Titans movie!), and only one Aquaman movie.