There are so many superheroes! But what makes a particular superhero good? What determines whether their back stories are well thought out or not? What factor decides whether he or she is corny or not? Is it because they wear underwear over or under their pants? Why are superheroes like Iron Man freaking awesome and superheroes like Squirrel Girl freaking stupid?
Well first off, I believe backstory is very important. A good back story determines how connected you will be to the superhero. For instance (SPOILERS) no one really cared how rocket (the talking raccoon from Guardians of the Galaxy) became a TALKING raccoon. But as soon as Rocket raged in the bar in Nowhere we felt bad for him and thus became connected.
Next, what is his or her superpower? This greatly determines whether a superhero is good or not. A superpower must be useful and very cool. For instance a superhero who can eat 300 hot-dogs in under a minute is neither useful or cool. On the other hand a superhero who turns into a large, green, rage monster and is practically invincible is all around awesome!
The Hulk brings us to another factor, the superhero must have a dark-side. Having a painful experience or event in the past were the protagonist made a wrong decision adds a great layer. Take Bruce Wayne i.e. Batman for example. Bruce Wayne's parents were killed in front of him. This was the root to his hatred of crime and opposition to killing. Batman would not be the same with that important detail.