[quote=Dervish]
I strongly considered Saren, but then I realized he only makesa handful of appearances in the game and you fight him twice. I honestly thought the Illusive Man was a far more captivating antagonist.
[/quote]

But despite the few appearances you do spend the entirety of the game chasing after him and trying to stop him, seeing the results of his actions along the way. You don't need to see much of a villain for them to be captivating. The more I think about it, the more I realise that in many games you don't see much of the main bad guys/bosses.