Narcissa Malfoy is certainly not a good character – but she's also definitely not as evil as her maniacal sister, Bellatrix Lestrange. Narcissa has always been a little more ambiguous; though she's haughty and condescending in public, she's always really just cared about her son, Draco. It seems like she might be kind of a middle ground between the wholly evil Bella and their good sister, Andromeda, the black sheep of the family (who ran away to marry Ted Tonks and become the mother of Nymphadora Tonks).
Once again, though she's on the side of the Dark wizards, Narcissa is primarily concerned about the safety of her family. We couldn't like Narcissa better than when she lies to Voldemort and saves Harry (we seriously never thought those words would end up in her Character Analysis) at the end. I mean, all the woman wanted to do was return to Hogwarts, find Draco, and finish this war so her family could remain safe. Though she's technically on the Death Eater side, it's her betrayal of Voldemort that makes Harry's eventual triumph possible.