You play as a human in nearly every game, humans are the baddies in sooo many games, a human is also the big baddie in sooo many games. So whats interesting about having yet another one on the pile? Why shouldn't the ruler/commander of all monsters not also be one himself o.o?
Don't that serve ta make him more menacing? Like facing the unknown? Rather than delving through some lame backstory and meeting someone who'll speak back at you like "look dude I get where you're coming from but you're doing it wrong so I'ma defeat you an save the land"?
I agree with the 1st paragraph, but not the second. Pig Gannon just ends up just being a larger version of the mindless, uninteresting, monsters you fight against in practically every fantasy game. It's hard to even imagine him as the king of monsters.
Now, if they made Gannon an actual character, then I'd be interested. It doesn't have to be a sympathetic story, just something other than a trite"I'm evil so I'm going to kill you!" Give him a believable and interesting character. Think about how the Giant Pig monster actually gets around. Then I'd be happy.