In the DC universe a superpower was never seen as anything but a gift. Superman was an escapist fantasy for boys about attaining ultimate power. He was the strongest being on the earth! He could fly! He only had one weakness and it was a substance that couldn't even be found on the earth!
For DC characters attaining a superpower was always a gift. it made you a better person and it didn't just give you more power it let you reach the zenith of that power. No one was stronger than Superman. No one was faster than the Flash. Superpowers made you unstoppable!
Meanwhile, in the Mavel universe, the Fantastic Four attain powers that scare the hell out of them and make them freaks in the eyes of the world. The scene where they realize they have changed is more akin to a horror movie than a power fantasy. Johnny Storm is on fire, Reed Richards body is seemingly collapsing on a moolecular level, he can't see his wife because she's turned invisible and Ben Grimm has become nothing short of a monster, a fact that will haunt him for the rest of his life.
These were real people dealing with real issues in a real New York. They beahved as a family would. They would fight and make up. They had money problems to worry about. And they had these messed up superpowers to deal with. The notion that a superpower didn't automatically make you an unstoppable force for good but could actually be a burden was phenomenal!
The formula was so successful that it would be repeated again and again.
Radiation made the Hulk the strongest being in the Marvel universe but it also turned him into a monster that the world feared and wanted destroyed.
Daredevil got an awesome radar sense but he had to sacrifice his sight.
And then the greatest of all Marvel creation's put the reader into the book like nothing at DC ever had. Spider-man was a teenage boy! He was the reader! An outcast at school. Lonely. He became Spider-man and lived the power fantasy for all of a few pages before the arrogance resulting from his new found power indirectly leads to his uncles death.
The reader could identify with Peter Parker on a level far beyond cool superpowers. And that was the fundamental difference between DC and Marvel characters.