Dark protagonists. Heroes who are evil, pure flaws, or exhibiting only weakness or darkness, rather than strength or light. There is one basic assumption I would like to make about such characters: they are unsympathetic, meaning the reader loses patience and interest with them quickly. I believe the majority of us can agree on this.
That being said, there are ways to write such a character so that the reader remains engaged. The method I have always used, which I learned from Donald Maass's book Writing the Breakout Novel, is to give the reader hope. Supply a small shred of evidence that the protagonist is not as dark as they seem, and are trying to be better. Essentially, the hero knows they are dark, and wants to change. This turns their darkness into a powerful sympathy-creating tool, and makes them much more interesting.
But not all novels follow this standard. In the Artemis Fowl series, the protagonist is a mastermind thief genius. He is undeniably dark and evil. However, he is not as dark as he would like to think. Certain subtle hints show that there is certainly hope for him.
Here's the problem: he doesn't want to change. If anything, he wants to be more dark and evil than he really is. This flies in the face of the above suggestion, which indicates that Artemis Fowl should generate impatience and eventual disinterest in readers. This is certainly not the case, judging from the sales, and my own reactions as a reader.
Obviously simply showing that a character is not as dark as they seem (even though they are still plenty dark), is a valid method for writing a dark protagonist. I am interested in how.
By all rights, Artemis should be abandoned by readers because he is evil and wants to be more evil. Yes, he is not entirely evil, but does he embrace the few redeeming qualities he has? No, he hides them. Certainly Artemis is conflicted, but that cannot possibly be enough. A reader should eventually get disgusted with a character who repeatedly drives himself into more and more evil. Shouldn't he?