I particularly like when a villain is, from their own perspective, doing something they believe is right and good --- except for the minor little detail of the consequences. Interestingly, these villains are NOT power hungry in the classic sense --- they may see themselves as the hero, bringing the world what it needs.
For example: in my current game, the Big Bad is a woman named Piloth. She has been an lich for a very long time, and deeply believes life itself is pain, and wants to free everyone from its grasp. In this game, once you die, a force immediately starts pulling on your soul (to go back home) --- so she really HAS been in pain ever since. Unless she's on unholy ground...
So, she will gladly murder someone and say something like "I understand why you resist. We fear what we don't understand. But, when you're freed from this pain, this existence, you will be free, forever."
To me, this is more realistic since most examples of day-to-day villainy come from people who truly believe they are doing what is right. They just think the ends justify the means. See any number of extremists for examples.
I guess these fall under the Anti-villain trope.
So I have no interest in the classic villain who does evil things for no reason other than For The Evulz.
Also, I think it's important to see how a villain affects the world at large:
Besides their loyal henchmen, these type of villains are supported by several Quislings (people who lust for power, no matter who has the reins), and the vast majority of people who just "go along to get along". Below is an example which might be from a now-long-cliched World War II empire:
"Oh, I'm just going to work, filling out some paperwork, attend a few meetings, and then I go home. I'm not taking part in the atrocities in the camp."
"Why didn't you do anything?"
"And risk my family's lives? For what?"
In other words, aside from La Resistance who are willing to risk everything to overthrow the Evil, the majority of people, even under the heel of a major villain, are more focused on living their day-to-day lives. This also explains neatly why there are only, say, 4 PCs who are willing to risk everything, except maybe for a small underground resistance movement.