If I wanted a villan that was evil for the sake of being evil, I'd be more akin to something like Gigyas or Majora. Entities of few words that want nothing more than to destroy, or conquer in some cases. "Creatures" can get away without having big motivation.
But if I'm dealing with a villan that is SOMEWHAT human and has clear reason and motivation, and can CONVEY those through words, I'm gonna need more than "Take over the world". That's Ganondorf in most cases. Whenever he babbles in other games, I don't feel afraid, or angry, or ready for a fight, I feel "Ugh, can't mash B fast enough, shut up so I can kill you." That is not a good villan. That is an object.
Demise vs. Girahim is a good comparison. Do people give a **** about Demise? No, you only see him at the end, he never antagonizes you or confronts you, you just hear his name here and there. Even then they barely talk about him. That is an OBJECT.
Girahim, however, is also evil just to be evil. But he has attitude. He's expressive. And creepy. He LOVES being evil for the sake of being evil. That's the difference: Monster Vs Human.
Hell, Ganon vs. Ganondorf is a good example. When I see Ganon, I'm all "That evil thing has to DIE". He's Ganondorf's power lust incarnite. When I see Ganondorf, I see a man. Er... Gerudo. A man needs to leave an impact on me to be more than just "A Man". OoT Ganon doesn't do that, you only really encounter him one in the middle of the game, then he takes Zelda right before the end. Twilight Princess he shows up at the end with no impact (Much like Girahim, Zant is far more interesting). Wind Waker? You SEE him at the beginning of the game. He sees you. Tosses you aside like trash. You hear the horror stories about him from the King of Red Lions. You confront him after fighting your way to the Master Sword, feeling more powerful. He once again tosses you aside like trash. You reforge the blade, and then find out he already is a step ahead of you. You enter his tour, walk up the staircase, he explains his plight and sends a puppet at you. You beat it, reach him, he once again overpowers you and tells you it isn't you he wants... eh, I'm just rambling at this point.
Regardless, you don't like him as much, that's whatever. Tastes are tastes. I just hate the "evil for being evil" argument. It's like in a cartoon when the antagonists say "Of course we are! We're the bad guys!". I hate that so much.
