Hearkening back to 2008, what made The Dark Knight and Iron Man so great was that they knew what kind of atmosphere was necessary for each scene and didn't try to craft a single dominant feeling over the entire movie. Disney, however, had already found their successful formula for live-action pictures via the Pirates of the Caribbean films; adventure-comedies. The thing is, while that totally worked for that franchise, it didn't fit the Marvel movies.
Iron Man 2 came off as ridiculously campy compared to the first entry, while Thor and Captain America didn't do any better. But the real damage arrived with The Avengers: it literally felt like every few minutes, someone was saying a lame, cheesy one-liner, from, "Sir, put down the spear" to "Doth mother know you weareth her drapes?" On the other end of the spectrum, Bruce warning Alfred he'll tell the police Batman was Alfred's idea is hilarious. Lois telling Clark to be careful with her bags because they're heavy is ironically humorous. As charismatic as Robert Downey Jr. is, Tony asking: "Of the people in this room, which one is; A. wearing a spangly outfit, and B. not of use?" just doesn't hold up to what should actually be a mature film.
What doesn't make sense is that all these movies come courtesy of several great directors/writers. What happened? Well..