Your mannerisms and choices will affect how your companions feel about you, but instead of only rewarding the player for placating, say, your friend Anders' desire for all mages to be free from the Circle, you also gain benefits from a contentious relationship. Get far along enough on either end of the spectrum from Friend to Rival and your companion will receive strong (and distinct) bonuses to combat.
I love this system, because it encourages you to make solid roleplaying decisions early. If you waffle and try to make nice when you actually can't stand Anders and his heavy-handed "Mages rock!" political stance, then you get no benefit at all. If I've learned anything from a lifetime of RPGs, mechanics that support storytelling and vice versa are the goal of all good game design and Dragon Age II manages this perfectly.
Gosh, yes, because pushing players to be ALL ONE WAY or ALL THE OTHER WAY is such a huge advancement in roleplaying. Balance and nuance is obviously a weak roleplaying decision, don'tchaknow?
Did I mention that lack of a third option was one of the things I really really hated about KOTOR? Especially given the complicated backstory of the protagonist of the first game, there were possibilities for several quite meaningful plotlines as we moved towards the endgame which were all cut out in favor of Good Or Bad, Take Your Pick.
For a series for which grey areas were a theme ingredient in the first entry, this is not an appetising advertisement. Of course, this is more a whine at the reviewer than a whine at the game, as it's possible (I don't know yet) that making choices that keep me in middle ground with a character will still lead to a satisfying roleplay experience for me.