I'm sort of conflicted. On the one hand, I like when companions contribute to quests in more than just passing commentary, but at the same time, it can sometimes be kind of irritating. In ME1, it was annoying when I went to get Wrex's family armor, but it was inaccessible because I required a more tech-y team, so I had to trek all the way back to get into the Mako to go back to the Normandy, and return with a team that would allow me to get it, meaning I had to drive all the way back for this crap. Wrex had some nerve pointing a gun at Shepard after running that kind of errand XD
The rest of the time, it was just crappy encrypted loot and terminals, many of which were missions I could just acquire some other way.
But as far as dialogue goes, I can't say that I'm the biggest fan. Like, with Varric and the slaver that has Feynriel, that would've been a good case for a stat that allows us to unlock special dialogue to be more persuasive, rather than relying on a surprise addition that includes an optional companion, because in that case, it's just to showcase Varric being a good liar, but there's no reason why we couldn't build our PC to be a better liar too. Though I do adore the class-specific response to dealing with the slaver. Knife to the throat. Friggin' sweet, that is.