Here's an excerpt:
But here's the interesting thing: Dexter is without a doubt likable. Why is that? Has Lindsay hypnotized us into thinking his psychopathic protagonist is likable when he's really not? Is part of his appeal that he satisfies his bloodlust by killing really bad people? No, I'd say Dexter is likable because he wants to be good, but he struggles with it. In his own twisted way, he wants to do the right thing even if it is untoward and disturbing.To read the rest head on over to: Make Your Protagonist Likable.
To make a protagonist likable, even one who's not a model citizen, give him an inner conflict between serving a greater good and satisfying his own self-interest. That sacrifice your protagonist makes to forego his or her own selfish desires and indeed serve the greater good is what makes him or her likable.