Don't you find a great villain is one whose motives are delineated, clear, complicated, and human?
No.
And my answer on considerable reflection is -- Maybe, there might be some definition of "great villain" such that these are the greatest of villains -- but who wants to write such "a great villain"? The aim, surely, is "a great story," and you want to have the villain that serves the story best, whether he's a "great villain" by that definition or not. He might be, I've read good stories where the villain was as complex as you please, but that it is a hallmark of the "great villain" in the sense of "the villain of a really great story" -- I deny it entirely. Indeed many of the greatest villains give off more of an air of a force of nature than of complex characterization.Consider some classics of fantasy. J. R. R. Tolkien's The Lord Of The Rings. Are Sauron's motives vivid and human? He only features in one scene, where his motives toward Pippin are clear but hardly complicated; for the rest of the book, we see only what we can deduce from his actions, or rather the effects of his actions.
Peter S. Beagle's The Last Unicorn. We see rather more of King Haggard than we do of Sauron, but while his actions all seem to be consistent for a single character -- even up to picking up the infant Prince Llyr and adopting him -- we don't get a deep insight into his character. Indeed, he has quite a bit of the air of a force of nature -- one of ruin and destruction -- about him.
Poul Anderson's Three Hearts and Three Lions. What are the Fair Folk up to? Nothing good. And plenty creepy. But the scene after they sent a knight after him and it proved to be a hollow suit of armor, when one of them mischievously declares that he's just going to have to live with not knowing, is typical of their motives. Or Operation Chaos. The little guys who cause trouble in each of the incidents have clear motives. But the big guy, behind it all -- well, Anderson describes him once as "the soliphist". A perfect gem-like description of his character -- but it's not a deep characterization.
