There's a difference between being "evil" and "eeeeeviiiil"; the latter is quite insane in concept, as how many people (short of those truly mad) do things because "I'm evil and this is what evil people do." I've heard it best explained as everyone is the hero of their own story, which is both fair enough and accurate enough. Most stereotyped villains have no motives really but evil, or their motives are so transparent and phony that they are just hollow excuses to not come across as two-dimensional.
The awesome, great villains?
As stated before, the "good" bad guy - or really, the antagonist done well - has a valid reason and purpose for what it is they do, or have rationalized it in a way within their mind. For some, their conclusion might be illogical, making the villain's thought process flawed or showing signs of obvious mental illness. Others? Others are that grey area, wherein they might just be right. They might actually be the "good" guy. Some might skirt being more obvious in that realm by making what I would call as "decidedly evil actions".
It isn't often, for example, that a heroic ideal is to kill the "bad" guy. A lot of morality teaches (most) society to provide mercy or grace on someone and while it isn't always followed through, a lot of notable characters flat out refuse to kill a villain on moral grounds alone - for better and worse, no less.
But the "villain"? You can name any number of reasons or come up with conclusions as to why the character does what he or she does. If done well they're not a villain so much anymore as just the "antagonist". They're not really the "bad" guy per say, but certainly aren't on the side of the (often) obvious "heroes" and or protagonists.
That said, do I love the antagonist? Absolutely. My favorite archetype to write for is the non-heroic antihero whose goals are morally ambiguous as to if they're actually right or wrong. It feels the most natural and credible. Certainly more so than "eeeeeviiiil!". As an added note on this portion, it strikes - myself at least - as most "evil" when a character who truly is ambiguous does terrible, horrible things but rationalizes it to the point they accept it and then gleefully employ it. Sadly, that is fairly common in the real world too.