Prophesies and chosen ones is a rather gimmicky way of controlling the course of a game. Everything must be done to preserve the illusion of freedom IMHO.
I'm partial to detective work myself, Like old style adventure games. The main plot doesen't have to be a constant running your head against a brick wall, but a wealth of disoverable bonuses that aid your progress in the game or just reveal something new. I like that a lot. It also gives the player a real sense of accomplishment instead of feeling led by the hand. If it's too hard, well, thats what the internet is for.
The spells you get from in depth discussions in PST, turning ppl to the dark/light side in KOTOR, etc.