Two, Marvel characters faced real ethical problems. They had to make hard decisions. Sure, it was comic-book style. We're not talking Shakespeare or Steinbeck here. But still, it was better, more engaging, than Superman vs. Lex Luthor, whose conflict boiled down to "Good is better than evil because it's nicer" as opposed to "Evil is better than good because it's more fun." You could almost root for Magneto, or feel sorry for Doc Ock. It was possible to empathize with Wolverine or the Hulk, whose biggest challenges were staying human, controlling the beast inside.
**** For example, http://www.ajc.com/news/nation-world/prosecutors-aurora-suspect-made-1505651.html