4. The Commitment
The best villains are driven by singular motivations - whether on a huge scale (to take over the galaxy, like Vader) or something smaller, though no less diabolical. In fact, it is the commitment to the cause and the conviction to the target that defines both great villains and great heroes - both deal in extremes by definition - and though Harrison's arc does change somewhat dangerously in the final act for the purposes of narrative impact, his bloody-minded devotion is what makes him hugely dangerous. He is a threat, defined by a deeply personal link to his agenda; a lot like a lioness guarding her cubs from attack, though simulatenously committed to an all-out blitzkrieg attack that is both devastating and awe-inspiring. His target is an impenetrable, iconic institution - just as Skyfall's villainous plot took down MI6, and the boldness and the downright arrogance of his agenda is what makes him such a sizable threat.