WARNING: This post contains spoilers.
Marvel has a license to print money. The Avengers is the 3rd highest grossing film ever in America bringing in about $625 million dollars. Its first follow up in this Avengers franchise was Iron Man 3. Shane Black's version of Iron Man is the 14th highest grossing film all time racking up a little over $400 million domestically. Thor: The Dark World did alright as it brought in a little over $200 million. Marvel's newest film in this franchise, Captain America: The Winter Soldier, has (as of the writing of this post) has brought in $200 million within its first 3 weeks. America can't get enough of what Marvel is producing. The problem, is that these 3 Marvel films since The Avengers have not been very good. Iron Man 3, Thor: The Dark World, and Captain America: The Winter Soldier are all not good films. Despite the praise and (for some reason) the high Rotten Tomatoes score, these are not good movies.
Now in fairness, the only Marvel film in this franchise before The Avengers worth a damn was Jon Favreau's Iron Man. I think Edward Norton's The Incredible Hulk was excellent as well, but the Hulk series seems to be culturally adjacent from the Iron Man/Thor/Captain America/The Avengers films. Iron Man 2 and the original Captain America and Thor flicks were not very good either. They were great to help set up The Avengers, but on its own, they were just "eh".