My own Opinions. Many of which agree with the above.
1. How reactive are the companions in DA:I?
Your Companions will Approve/Disapprove based on your choices, and will talk to you about plot points, but they won't actually refer to what you did they Approved/Disapproved of. It's like they just did 1 dialogue recording.
Of my different playthroughts, I only recall 1 big argument with my advisors and 1 noticeably different reaction. Otherwise it's like the same conversation every time.
2. How multifaceted are the companions in DA:I?
Somewhat. Everyone has skeletons in their closet, but they're all pretty trope-ish, like the typical nice guy harbouring a dark secret sort of thing.
Of the 12 Companions and Advisors, I only found 1 was really surprisingly multifaceted, like it caught me off-guard how much there was beneath the surface. And 1 other one that was deeply disturbing, like I already knew there were dark secrets, but the depth of which scared me like how sinful that person was.
3. Does DA:I handle choice and consequence? Is it noticeable?
Sadly, not well. Like when you choose 1 faction over another, it ends up being the same quest either way just with different enemies, but they go through the same motions.
In other words, I could make a big decision, a major plot one, and I'd actually forget what I chose as it so didn't matter.
4. Does DA:I do a good job at providing multiple solutions or approaches to the conflicts in game?
Multiple solutions, pretty much the same results. More like an illusion of choice.
5. Does the ending to DA:I provide a deep sense of catharsis like in DA:O?
Absolutely not. It asks more questions. Which is actually exciting. It's not closure, it's "what's next?"
6. Can you converse with companions anywhere or are you restricted to having meaningful conversations in the "party camp"?
Very party camp. And of the 12, only 3 party members are so much fun I would want to talk with them between every mission.
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I sound very negative, but it's only because I am answering your questions directly.
If your question is, is DAI worth it? My answer would be a huge yes.
What they get right, they nail it so perfectly it's worth the price of admission IMHO.