I think "how evil" a villain is/should be really depends on the story and the intended audience. Not that you can't have complex villains in "kids" media. Just look at Avatar: Fire Lord Ozai is really super bad, and the moral questions that show gets at certainly aren't typical of those seen in a lot of "kids" shows. But that complexity is part of what makes it so successful.
In that vein, to me, the best kind of villain is complex. They aren't bad just to be bad; they have a reason for their actions. My favorite kind of villain is one whose reasons are powerful enough that you almost support them--a well-intentioned extremist, if you will. If they truly believe their goals are noble--even if their actions aren't--it makes it all the more tragic.
Sometimes you want bad guys just to be bad, though. I really love it when a villain is portrayed at first as being actually an okay person (just heartbroken or driven to some kind of extreme), but then the plot twist reveals that they're actually just a psychopath. I LOVE THAT SH*T. To be honest, I think villains are often more interesting than heroes.
As for the villain of my comic, she hasn't been introduced yet so I don't want to say too much about her. The main antagonist for the first part of the story, on the other hand, has been introduced. But 'antagonist' and 'villain' aren't necessarily synonymous. I can't say more because spoilers, but I will say that Reus deals with areas of grey morality and questions what justice truly is. How do you do the right thing if you don't know what is right? Anywho. The villain is definitely a villain, but a complicated one.