What distinguishes a superhero from a plain old "hero" are superpowers. The ability to fly, super-strength, heightened intelligence, etc. all qualify. Otherwise you're just a do-gooder who would likely fall victim to a Green Goblin pumpkin bomb or Doctor Octopus' tentacles. You need honest-to-god powers to compete in this universe.
After being bitten by a radioactive spider, Peter Parker gained the proportionate speed and strength of an arachnid, as well as the ability to scale walls and jump long-distances (contrary to the Spider-Man movie, in the comics, Peter was not able to produce his own "webbing." He used his scientific know-how to engineer mechanical web "shooters"). But the superpower that always stood out to me was his "Spidey Sense." This power was an innate warning system; if a villain was in shadow ready to strike, or a floor board Spider-Man was walking across was on the verge of collapse or revealing his position, his Spidey Sense would "tingle," enabling him to use his lighting-quick reflexes to get out of harm's way.
When I was much younger and still trying to determine which heroes I most identified with, these distinguishable superhuman traits were vital. Superman was almost too perfect - stronger than everything, immune to bullets with only one real weakness, a foreign substance from his home planet called kryptonite. Sure, villains always found a way to procure kryptonite to keep things exciting, but as a kid, I viewed Superman as indestructible, even when DC inexplicably tried to kill him in the 1990s.
I was also never able to get behind superheroes with projectile powers -- i.e. shooting fire, ice or water (thus negating a number of the X-Men). It felt like cheating to me. When the going got tough, they were able to lean on the power of the elements to get out of trouble. Plus those were the kinds of powers reserved for super villains. It was up to the superheroes to outsmart the villains, not match power for power.
You could throw physical freaks of nature like The Hulk and The Thing in a similar boat. Yes, Spider-Man has strength, but as you might recall, when he was buried under tons of steal and wreckage in ASM #33, there was serious doubt on the reader's end that he'd be able to power his way out. It took every last ounce of strength and determination for him to succeed. Superheroes like The Hulk and The Thing seem to get by just on brute strength. In the Ang Lee Hulk movie a few years ago, the green guy was swinging tanks around like they were baseball bats. That's just not fair.
But Spidey Sense is both simultaneously beyond the realm of imagination and realistic. While it's a clear advantage for Spider-Man, it's a power that makes sense -- a spider is comparatively strong and fast in the insect kingdom, but a key part of its survival is its ability to elude danger. How hard is it for a person to sneak up on a spider? If you're looking to squash one, you generally need the help of a newspaper or something broad. And yes, just because Spider-Man had his Spidey Sense, doesn't mean he never got hit. In the comics, he gets beat up on a regular basis. But the Spidey Sense still gives him at least some kind of an edge headed into a fight. Spider-Man still has to use his intellect and speed against characters like Electro who can control electricity or Sandman, who's more immune to physical damage because he's made of sand, but the Spidey Sense gets him in a position to succeed. And the Spidey Sense also helped Spider-Man vanquish perhaps his greatest villain of all time, the Green Goblin (before Marvel brought him back to life in the 1990s, but let's not get into that right now). After a knock-down fight in ASM #122, Spider-Man starts to close in on the Goblin when the villain summons his Goblin "Glider" to act like a guillotine and slice Spidey in half. Spider-Man's Spidey Sense tingles and he's able to dodge the sneak attack, leaving the Goblin to get the sharp end of the stick.
