Until I came to the BioWare boards and began to talk about companion interaction, I didn't realize that reading people and anticipating their reaction was a skill. I figured out what Isabela was like before I even booted up the game: fun loving, likes making money, likes freedom, doesn't like responsibility or being tied down.
My first game, I easily got a ton of friendship points. My second game, I easily got a ton of rivalry points.
If anything, I found Isabela a touch too easy. TOR is better with this as the companions tend to have rather complex rules for what they do and don't like. The first JC companion you get is part of a society of hunters, and has elaborate standards for when to help people, when to not help them, and when to offer mercy. The first four commando companions are all pro-Republic and military types, but have different ideas on when to follow regulations, when to bend/brake the rules, how much respect to show to an enemy, and who deserves to live and die.
If anything, I'd like Dragon Age: Inquisition companions to show that level of complexity when it comes to affection.