I view the successful superheroes from a more abstract perspective.

Powers of a superhero are, from my perspective, less important than the character traits that those powers enable to stand out, and the most consistently popular super-powered characters follow an archetypal ideal. Many popular heroes don't even have superpowers, or their superpowers are only adequate to allow them to confront the extreme dangers they face and survive without seeming contrived. Batman has no superhuman powers, Spiderman is strong, but is actually out-muscled by Kingpin, Wolverine's only actual "power" is his ability to heal from anything. Superman, who is absurdly powerful, doesn't come close to the popularity of any of those 3.

Heroes achieve enduring popularity by representing the same things that Heroes have always represented: Ideals of character and ability. In modern times, character is the more important of the two.

Batman's fulfills the character archetype of the Knight. He is wealthy and martially skilled, and that wealth and skill goes toward the pursuit of justice and the protection of the defenseless. To add to this, he has a fixed moral code which he does not break for anyone. Regardless of weather you agree with the actions of a particular iteration's Batman, if he's done well, you are left unable to [i]not[/i] respect him for holding to his code in his own actions. He's not known as "The Dark Knight" for nothing.

Spiderman is actually both the Everyman and the Nerd. While he has powers, and wants to do the right thing, he is constantly struggling to make ends meet due to his self-adopted duties, and the "The Man" (represented by Jonah Jameson) is usually trying to keep him down and overall screwing him over. Addtionally, Peter Parker is a huge Nerd, and that is, in some cases, a far more important "power" than his strength, agility, or wall-walking. Remember that he invented the web-shooters. This togeather makes Spiderman the most relatible of any super-hero, and is the empowered audience surrogate.

Wolverine is the Berserker with enough Anti-Hero to keep from crossing over the moral event horizon. He's tough, gruff, and generally doesn't give a crap. Granted, he can heal through most any damage you can throw at him, but he can and, more importantly, [i]absolutely will[/i] keep coming if you piss him off enough. The best way to piss him off? Hurt a bunch of innocent people and/or his few friends. Wolverine represents the raging, righteous fury that we've all wanted to dish out at some point in our lives when we witness some willful act of blatant evil. Sometimes our moral outrage leaves no room for thoughts of "mercy" for the perpetrator, and out instinctive side cries out for violence; this is Wolverine.

Superman, in all honesty, is the Messiah. He is litterally not of this world, though he clothes himself in it's trappings. His motives and methods are generally pure as the wind-blown snow, and his raw power outclasses virtually anyone in the entire DC universe, with only a handful of entities that even pose a physical challenge to him. They have to include Kryptonite just to provide plot tension more than half the time any more.

Captain America is the Patriot. The patriot can theoretically apply to any nation, but in this case, he is the epitome of American ideals, if not an accurate representation of the state of the nation in actuality. This is most obvious when his character opposes the actions of the American government when it violates the principals of democracy, liberty and equality. Captain America is a character that reminds readers of the values embodied in the Declaration of Independence and the Constitution, even when the people around him falter towards tyranny.

Hyperbole is important, as stated earlier in the thread, but it much more important to first establish what ideal you are going to apply the hyperbole to. When making a great superhero, it's important to understand what character archetype you are creating, and how to tell the story of the character to give an audience something to idealize. Flaws are important for grounding a character, but don't flaw the ideal, flaw the other aspects of the character, or else you risk crippling the Heroic aspects of the story.