I liked it in Conan the Barbarian.  The bad guys killed his parents.  Now it's revenge time.

Maybe from the games you have played they are crap, but that doesn't mean that there aren't any good ABS's around.

Examples:
http://www.youtube.com/watch?gl=GB&hl=en-GB&v=tiKdUJx42DQ&feature=related
http://www.youtube.com/watch?v=qmnD-4dYZkY&feature=related

http://www.youtube.com/watch?v=f7SotgdE824

HOLY CRAP

I like that idea too, but I think it would be a cool extension to the idea if the player didn't know they were being tested - ie put them in a situation that requires them to make decisions (not literal ones) and then come up with an algorithm that suggests a class for them. If I were to implement something like this I might not even tell the player that any of the above happened, nor make it known they're even in a class based game.

Yeah, I like that.  Maybe you start-off with a default character, and your various moral decisions and whether you favor fighting / magic / healing determine every subsequent character that joins your party; and after not long, the default character gets killed off, leaving you with just the customized characters.

I got this terrible idea for a custom feature where the game has a built-in i.q. test where your caster's intelligence / mind stat correlates with the i.q. test score.  Then a mini-game that is effectively an agility test, where your rogue's agility stat correlates with the agility test score.  I immediately decided it probably wasn't a great idea, but who knows, someone else might like it.