You see DA: I is my least favourite game (but still good, and is the easiest to replay) because they've reduced the role of side-quests. In DA: I, you stumble across a side-quest in the field via a random letter, and literally your only option is to do it or not. If you stumbled across a side-quest in the other two games, you get to talk to the person, see their motivations (with opportunity for sarcasm), and then decide to handle the quest straight, do it but then screw the guy over, persuade out of fights, bribery, etc.
For me, DA: I really suffered in my opinion because of that. They function as EXP boosts, as opposed to meaningful bits of story.