Video games, by their nature, are about some kind of conflict. That conflict can take many forms. You against another player. You against the clock. You against the score. You against yourself. And, of course, you against the malevolent evil that threatens the very existence of your town/family/planet/spaceship.
This is nothing intrinsically new to narrative structure or even to our basic ideas about conflict. Man versus man, nature, fate, self or whatever other form of antagonist you care to classify — these are the basic building blocks of pretty much every story anyone bothered to expend breath telling. But unlike such things as movies and books, where the experience is a passive read on the story happening to and through a protagonist, in most cases with video games the hero is always in some way the same person: some version of you.
Now, you may be represented in different ways through the game, perhaps as a sexy elf or a gun-wielding dispatcher of unearthly evils (who is also sexy), but ultimately, when you play, you are filling a skin. Underneath, it’s still basically you. In some ways, I think this ultimately diminishes the value of the hero’s narrative — not eliminates, mind you, just diminishes. After all, it can be hard (though not impossible) to paint a complex central hero, when ultimately that hero had to have enough space inside for your ego to insert itself.
But while the hero in many cases has to be defined by and fixed to the player, the problem with villains in games is almost the opposite. It can be literally anything.