Playing two-dimensional evil for the sake of evil is boring. What attracts me to playing the bad-guy is the diversity it has: it's also a reason many, many Hollywood actors say thery have the most fun playing The Heavy. And why many comic book villains are more interesting than the good-guys.
Look at Dr. Doom for example. The man ruled his country with an iron-fist, but he also improved their standard of living and they, for the most part, loved him. His view was that he could rule and improve the world better than the U.N. and other world powers were doing.
Magneto: A man that actually cares about his species, and sees the subjugation they suffer at the hands of humanity as a direct correlation with what happened to his family in WW2.
Lex Luthor: A man that believes the future of humanity, our evolution and accomplishments, should be decided by humanity, not some alien with God-Like powers.
Two-Face: A man literally torn between the two facets of his personality/mental disorder.
How about Anakin/Vader? A Jedi Knight that felt stifled by the Jedi Order, yes. But also a man that would have done anything for love and to save Padme, including selling his soul to the Dark Side. A young man that also believed the Empire could end the civil war with the Seperaltist and bring peace to the galaxy. Good intension, for sure, twisted by Palpatine and the nature of the Dark Side.
Not every villain need be the typical psycho, ala: The Joker, Deadshot, Deadpool, Sabertooth, Bullseye and others.
Just as often, a well developed villain can, and should, be more interesting than his/her counterpart.
For that reason, I am looking very forward to CoV and the chance to create my main-hero's (and my SG's) counterparts.