Some fictional heroes are good. They resonate with us and inspire us long after we have finished reading or watching. Luke Skywalker, for example.
Other heroes aren't so good. They're forgettable or, even worse, turn us off to the point where we abandon the book or walk out of the theater.
So what makes the difference? I think it's three things:
1.) The hero should be a decent human being. He shouldn't be a dick. He shouldn't be cruel. He should have a conscience. He should be motivated by positive, uplifting desires, what is best in all of us. Basically, he should be a role model, more or less. Most readers would rather be inspired than stare into the abyss.
2.) The hero must be sufficiently challenged. If the obstacles of the plot are too easily surmounted, then the story is boring. Anyone can "overcome" when it's easy. Heroes overcome when it's hard. That's what makes them heroic in the first place. If your hero never fails, or never gets injured, then you're doing it wrong. Luke Skywalker got beaten and knocked out by Sand People, was thrown across the cantina by ruffians, got zapped by the Force-training remote on the Falcon, and was strangled and half-drowned by the garbage monster before he actually accomplished anything important. In short, he took his licks. Make sure your hero does, too.
3.) The hero must solve the main plot. Too many books end in cliffhangers nowadays. I don't like it. I think it's disrespectful to the reader. If a reviewer mentions that a book ends in a cliffhanger, then I won't download the book. It's as simple as that. I want stories with beginnings, middles, and ends. If you must have a hook at the end for the next book, then do it in the form of an epilogue. But always solve the main plot. Give the reader a satisfying conclusion first. Then you can hook him for another book.
These seem like pretty simple criteria. And I suppose they are. But I'm constantly seeing authors who flout one or more of them. Those authors are often oblivious as to why their works aren't more popular. I think such authors would find that adhering to these three rules would make a world of difference in their books' success.
I've been guilty of breaking these rules myself. Writing good craft is a never-ending struggle. But I know my weaknesses, and that's the first step in overcoming them. Hopefully my readers will think I've succeeded.