I remember finding out when "Avengers: Infinity War" was coming out and how it would combine almost all of the Marvel superheroes into one epic movie. Now, I'm a sucker for a good binge session, so I set out to watch every Marvel movie before I saw "Infinity War."
Every superhero movie might have a similar premise: the good guy beating the bad guy, but Marvel movies have something distinct about them. They humanize these heroes. From Tony Stark possibly having PTSD in "Iron Man 3" to Peter Parker just dealing with being a teenager in "Spider-Man: Homecoming" these movies have shown that while these people are able to save the world they are still dealing with real-world issues. One of the pioneers of this concept was Stan Lee.
I'm not well-versed in comic books by any means, but I've seen enough panels of old Marvel comics to know that these characters were created with these problems because of Stan Lee. He had a concept that just because they had superpowers didn't mean they didn't have problems. He gave emotion and life to characters that could have just spent their comic book days fighting villains in every page.
These personalities translated well on screen too. I can think of very few people who would want to go to a movie and just watch one long fight scene. Giving heroes actual personalities allows them to have more range in their own stories. It's the reason "Avengers: Infinity War" made people feel the emotions it did. Audiences probably wouldn't be as torn up as they are if (spoiler) a bunch of bland, humorless heroes just disappeared at the end.
It didn't take long while watching all these Marvel movies to fall in love with the heroes and their whole universe. We wouldn't have one of the biggest movie franchises in history without these characters, and especially not without Stan Lee. Excelsior!