I think Narcissa is evil, as is her husband, but not extremely so like instead of killing left and right, she casually mentions to Lucius someone who pissed her off that afternoon and lets him handle it. This generally applies to most of the 'dark' characters but I like that they are evil because if everyone was secretly good, that would be boring. Let the goods be good and the bads be bad.
She's a snooty bigot and that would makes her awesome because she gives no apology for it. She didn't save Harry because of inherent goodness and he will save them all and yadda yadda, she wanted to save her son. She knew, observing from like book 6 onwards, that the Dark Lord was absolutely nutso and having the likes of him in charge will lead to their ruin. I mean come on, he mangled her husband's wand, sent her son off on a suicidal mission, turned her home into a den of torture, she wasn't going to put up with that forever.
All that said, I like Narcissa as I like most of the Dark contingent [yes that includes Voldie] because they just are. She doesn't make excuses for what she is and just goes on doing what she wants. I always had a thing for the shamelessly bitchy characters. smile