As it turns out, superheroes are a bunch of egotistical douches.
They are very concerned with their rankings and they'll do anything to level up, which kind of sucks, because they have to act on a regular basis, not just when they must. They're also extremely jealous of other, more powerful superheroes and hold them back whenever they can.
The only character who is not an egotist is Genos, who's humble and willing to sacrifice his life for a greater cause. Unlike other heroes, he gets perfect scores because of hard work. He's a respectable character, probably the only one who invites any kind of sympathy. He acts and talks like a true superhero, yet is just Saitama's side-kick by his own admission, which relegates him to the supporting cast of characters.
Then there's Saitama himself, who's lazy and bored. His disillusionment is understandable, because he became a hero to avoid work or boredom, yet regularly fails to escape both. Voice actors Makuto Furukawa (in Japanese) and Max Mittelman (in English), make Saitama actually sound like the most bored superhero ever.