Who needs a villain when you have Steve and Tony? Both protagonists. Both antagonists. And drawing other power-people to their cause in surprising ways. The clashes go far beyond the set-up squabbles of Avengers Assemble. Or even that other big 2016 superhero showdown. Forget Batman v Superman. Here you get Ant-Man v Spider-Man, Hawkeye v Black Widow, Scarlet Witch v Vision, The Winter Soldier v Black Panther and (well, duh) Captain America v Iron Man, all rolled into one. And that is what you call the ultimate Marvel superhero event.
I don't like the Marvel universe and only see it as a series of movies that help increase the budget for any future Star Wars movies, but this is what happened when a studio has some sort of quality control. Take note, WB!