Neo Darkhalen
Mission zero
i think it depends in what context you are looking at, what makes a good villain for me is complexity in that they have multiple layers, they have real goals and desires, so you can identify with them a good villain should be able to inflict different emotions to the audience and make you think, they need to have there own will there own style and thoughts, a smart villain is always one to do this, however i think a villain should be well established to the case of the story, so if it's about planets being concerned the story should give hints or history to the villain before they are introduced and on that case i believe a villain should not be forced into a story just for the sake of them being there, his or her inclusion should flow well and have an impact with the story.
And on a last note i believe another good class of villain is a tragic villain these villains always make you think and at the end you are sad to see they have failed, they always manage to challenge your morals.