Would it still be an interesting story if you did always know what was going to happen next, though?
That's not the issue. I have *no* idea what'll happen next in AtF. Anything is possible, literally. But everything that's happened (pretty much) is because of Angel's actions, and those actions have been very in character. Buffy robbing banks is *not* in character. I'd rather she'd set up a lap-dancing club. At least then the money would have been honest.