Robert Downey Jr.’s Tony Stark/Iron Man is the main character of this series, but Chris Evans’s Steve Rogers/Captain America is its beating heart. From this trailer you can see the outlines of the story—the world is scared of super-powered beings and wants to control them, while Steve Rogers is skeptical of governmental authority and only wants to do what’s right, no matter the fallout.
But the moment that really gets me is when Captain America says to Iron Man, “I could do this all day.” That’s a callback to the first “Captain America” movie (which I also recommend highly—it requires no knowledge of backstory and is a delightful throwback to World War II propaganda in style and shape), a pivotal scene where a scrawny Steve Rogers refuses to give in to a bully who is beating him up in an alley. Many movies (and 80 years) later, he’s refusing to give in to a new bully—Tony Stark.
Plus, y’know, my favorite superhero of all time appears in the last five seconds of the trailer, finally able to pal around with the heroes from the Marvel Universe again. So that’s a plus.