@absolitude: The way that I see it is a character can go from hero/villain/anti-hero /anti-villain in a matter of seconds, and all it really depends on is their actions within a current situation.
This can make it tricky to understand where on the scale of good and evil do some characters fit.
You get the impression that DmC Vergil is doing the right thing, but he's doing it more for himself, and for his own intentions. That's why up until the end he cares about his brother, is by his side, and even saves him from death. However, as soon as he's aware that Dante wants no part in his plan, it's "you're either with me, or against me". Not to mention that Vergil probably wouldn't bother to save Kat if it came to it, whereas Dante would. This clearly shows Vergil's true nature of selfishness, and ruling the humans wouldn't be about protecting them as much as appearing superior to them. I mean, Kat regarded him as a close friend, and Vergil practically insults her by calling her (alongside the rest of humanity) weak.
My big problem with Vergil in DmC is his attitude.
DMC3 showed off a cool collected Vergil whom at the very least respected those weaker than him, even if he believed himself above them. Vergil in DmC is a selfish child by comparison, consumed by only himself, whereas in DMC3 he was atleast defined by his principles i.e. 'this belongs to a son of Sparda' 'without power you can protect nothing' etc.
I would actually say, Vergil in DMC3 is an Anti-Hero throughout whereas Vergil DmC is a villian, he didn't transform to become a villian in the end game, the result would've been the same if Kat/Dante hadn't played along like good toys from the beginning. But, I agree, defining an anti-hero is a messy subject with plenty of factors to concider -- I feel it must come down to their divinity - wether they would DO good if they had to, or not. I don't get the feeling that DmC Vergil would've saved Kat or Dante unless it suited his plans, an Anti-Hero such as Shadow (trying to stay consistent) would save the Hero because he knows it's right but not nessacerally because he wanted to -- it would probably get brushed off as "well now you OWE me one" or "that makes us even" or "don't read to much into this...I need you alive so *I * can kill you later", that sorta thing.