Justice League was a disappointment.

Well, they both featured a villain who was a God from another planet with a Horned Helmet who was looking for a powerful cube and had an army of alien troopers.

One difference was that Avengers didn't stupidly overpower its heroes to the point all drama was lost the way JL did. JL had to make WW and Flash utter incompetents so Batman wouldn't look totally unnecessary and then Superman just killed all tension anyways.