To me, a good story is one in which I care what happens.
If a writer can’t make a reader care they have not done their job. It doesn’t matter what genre it is, or what it is the reader should care about. The protagonist could be saving the world or saving a lost puppy. Success must matter to the reader.
It doesn’t matter if it’s mastodons, crinolined ladies, car chases, housewives or aliens from outer space, the reader must care about them. It helps a bit that many readers keep to one or two favorite genres. The writer doesn’t have to worry about a chick-lit reader caring about a robotic werewolf because that reader isn’t going to be reading that story.
Within your genre, what makes the reader care about a character? Is it strength? Beauty? Intelligence? Probably not.
It’s having them face up to difficulties, often of their own making, and struggle in a way we can identify with to a satisfying conclusion. The writer needs to grab the reader right at the start and give him a reason to care. The protagonist shows basic humanity, he makes mistakes but he heads in his true direction.
The protagonist is a three-dimensional character – he has a mental, physical and emotional life. We might not agree with everything he stands for but because he has been shown in all three dimensions we are likely to go along and enjoy the ride with him.
The worst thing your reader can do to you is stop reading. The best thing is for him to keep reading even though some other thing should have been his priority. You are a success as a writer if the reader is so into the book that he goes past his stop on the subway, or forgets to cook dinner. (“It’s pizza tonight. OK? Save me a piece – I’ll be right there when I’ve finished this chapter.”)
Let your protagonist capture and captivate your readers. It will keep them coming back for more and they’ll tell their friends “I always like this writer. I know it’s going to be a good story.”