Each of your companions have their own personality and beliefs, and it can be fun to listen to them argue with each other throughout the course of the game. Fans of the Star Wars: Knights of the Old Republic series should recognize this system. The decisions you make also affect how they view you, so if you constantly intimidate or threaten NPC's, your goody-two-shoes companions will get upset with you. Upset them enough, and they might even leave your group.
You will have a hard time pleasing everybody, though, as it seems that every decision you make increases your influence with one of your companions, and decreases your influence with another, which makes keeping your party members happy almost impossible at times. Making it worse is that if you want to learn more about your companions (which can sometimes lead to them multiclassing and broadening their abilities), you have to increase your influence with them. Since influence is constantly going up a point, then going down a point, its probably best not to try and please everybody at once, but to instead focus on one or two at a time. As you learn more about your companions, optional side quests open up revolving around those companions. These quests are good for rapidly increasing your influence with a particular character, assuming you make the correct dialogue choices during the quests. 