His methods included cruelty and torture, but from his point of view it was all in service of a greater good.
Again I ask, WHO CARES? Some things are indisputably, objectively evil. Some points of view are simply, obviously wrong.
I'm not saying otherwise.
I'm merely saying that a character whose sole motivation is "I must be EVIL to move the story forward!" is boring. Give him something to care about, something to drive him, even if it's obvious his perceptions and conclusions based on that are twisted.
Nero got a revenge motivation. Simple, fairly prosaic, really, but it was something. He's not as flat a villain as some I've seen, but there's just not a lot to say about him.