1. An awesome hero (obvious, yes, but it must be said). The less obvious thing is what constitutes a good hero. Personally, I think perfection is highly overrated. If you've got a hero without flaws, you've probably got no story (or, at the very least, one with the depth of a teaspoon). Oh no! A giant monster rampaging in the city? Piece of cake for your hero. A huge meteor is about to collide with the planet and destroy half the population? Forget it. Mr. Perfect took care of it ten minutes ago. An evil mastermind has a genius plan to take over the world by turning everyone into zombies? No big deal. Ms. Infallible already knows how to stop it.
Vulnerability is the key to making a hero interesting. Call me crazy, but I like my superheroes to mess up once in a while. Superman isn't always my favorite superhero when he's close to perfect, but at least he's got his kryptonite. He's got to have a few setbacks when he's trying to stop Lex Luther. Iron Man started with the daily threat of shrapnel piercing his heart if he didn't charge the magnetic chest plate keeping it out. Spider-man was just a nerdy teenager dealing with the typical dramas of being an unpopular high-school student. It only took four bullets from a sniper rifle to take down Captain America, a guy who had survived decades frozen in a block of ice.
More than just a vulnerable hero, I tend to love a tortured hero. I think we all like our heroes with a hint of cynicism and questionable methods. The comic book world is full of anti-heroes that are tormented by either their pasts or some fearful insight into human nature, and the only way many can respond is to embody the chaos of the dog-eat-dog world. These are the most compelling characters in comics. Wolverine's visceral drives are a huge factor in his immense popularity. He doesn't always do things by the book, and neither do characters like Rorschach and the Comedian, to whom we are drawn and interested in despite his obvious flaws and seemingly unforgivable mistakes. It's always going to be more interesting to follow a character teetering on the ledge between heroics and wrongdoing.
2. A villain who would make you shake in your superhero boots. Sure, the idea of common burglars and muggers in everyday life may seem pretty scary, but knives and guns are pathetic in comparison to the super-powered or technically-aided vigilantes they're up against. A good villain needs to have powers, and those powers should probably be much greater than the hero's. Galactus may wear some crazy headgear (at least, he does as we meager humans see him), but he is the Devourer of Worlds, the embodiment of the cosmos so powerful that his true form is inconceivable to anyone. There is no way that anyone should be able to beat that, but that's the kind of thing that readers want to see the hero either overcome or be defeated by (the bad guys have to win sometimes). Of course, there's nothing wrong with intellectual powers either. Some of the scariest bad guys are the evil masterminds that are otherwise ordinary human beings.Often, a great villain comes straight from the past of his or her hero counterpart. Why are Venom and Carnage awesome foes for Spidey? They share the connection of being bonded with deadly alien symbiotes like the one (in the case of Venom, the exact one) that tried to bond itself with him. And you can't forget all of the family rivalry that goes on in comics, especially when a former good guy goes bad (whether under the influence of mind control or not). Nothing like having your wife attacking you, huh Cyclops?
3. Gray areas. Morality isn't exactly clean cut. Any comic that presents it any differently probably won't be a great read, because if everything is perfectly black and white (and I don't mean the artwork) there is no room for a hero to ever lose. This is one of the most captivating themes at the most basic levels of almost any good comic. The two best characters of Watchmen are personifications of the chaos created in gray areas between right and wrong. And Wolverine? Well, he eats your perfect morality for breakfast.
