From geek to great
Most superheroes can be called geeks in their normal human avatars. They are confused and timid before they receive/discover their powers. The way the powers change their attitude is worth watching/reading. And to top all of this, even with that nerdy attitude they date the hottest girl in college or the office. They set a precedent that "geek is not bad."
They rise from tragedies
The superhero's past is usually not very joyous. They have faced a series of tragedies which usually makes them emotionally strong. They can induce glory even from the smallest thing. This forms an interesting story behind their powers, and people love it. Another reason for loving superheroes is their positive attitude. The audience is impressed with the way they face the bad times and fight it out.
There is always a megastar behind the mask
It's not the just the mask that looks good, there is always a graceful face behind it. People are not only obsessed about the powers and the costumes, they are also crazy about their looks. Girls almost blush when they see the handsome face behind the mask, and boys root for the strong personality. The characters are awe-inspiring and they are carried very well.
They are clever
Be it a male or female superhero, here beauty comes with a sharp brain. They understand the plans of their enemies well in advance and always have a solution for it. Even if the situation turns worse, they find a way to come overcome it. Be it a strong enemy or the angry girlfriend, they know best how to fix both.
They are strong
Of course they are strong! No matter how strong the enemy is, they don't get intimidated. They know what's good and what's bad, and they don't ever make a wrong move. They stand for what they believe in, and it's always the correct path. Their virtuous approach impresses the audience and makes them fall in love with their powers.
Their well-designed costumes
It's not just the powers that make a superhero, it's their costume too. With amazing superpowers and an impressive personality, comes a perfect costume. They are the center of attention of the whole superhero series. The color, the design, and exceptional weapons are stunning. Superhero costumes form a part of their identity.
Their symbol or insignia
The common features of superheroes are an extraordinary costume, mystic powers, and a symbol or insignia (which is a must). A symbol is a superhero's ID card. The symbols are simple but attractive. People are such big fanatics of their symbols that they use them in key rings, tattoo designs, T-shirts, mobile/desktop wallpapers and what not.
An excellent sense of humor
Be it a life-threatening situation, superheroes know how to make it funny. They are experts in timing their words and passing witty remarks. They can ridicule anything, including their enemy's best moves. With their wit, they keep on entertaining their fans, and this is why they are loved so much. Not many people like to be serious, and thus, they don't make it serious.
They are honest towards their responsibilities
"With great powers comes great responsibility", and they believe in this fact. They are willing to sacrifice everything to save people. They are the soldiers in fancy costumes who have vowed to save the lives of people at any cost. People fall for their attitude and determination.
They are loved because they inspire us ordinary humans. Their good deeds set an example of kindness. They even encourage geeks by proving that they can also get the hottest girls. People know they are just fictitious characters, but they show how to follow the path of virtue. Though they have supernatural powers but then people start believing that you don't need to have such powers to be a hero.