I also thought companions were a tad more passive than the situation warranted - at the very least, I would have expected them to voice their opinion in the aforementioned mindflayer scene (e.g. "Kill it already and be done with it!" or some such). I suspect that that may be something that will be added along the way, since it was present in DOS2.
Also, companions don't seem to react to different player backgrounds at all. My character is a Drow cleric of Selûne (unlikely combination, I know), and Shadowheart, who as a cleric of a rival goddess should have hated her on sight, didn't even blink. In fact, the two of them are getting along surprisingly well so far.
