I didn't see a thread discussing this as specifically I wanted to post in without doing some forum necromancy, so here we go.
Needless to say, but this thread will of course cover MASSIVE spoilers and touch on delicate topics, so if you haven't beaten the game or cannot handle respectful discussion of delicate topics, this is not the thread for you.
Also, please remember no one has primacy of opinions. We can disagree without needing to force our opinions on each other.
Astarion: He was amongst my favorite reasons to play the game at first, I found endearingly obnoxious. After a few playthroughs though, I found his lack of sympathy for anyone not directly in his circles to be very hard to look past. He's a victim, like all our companions, but he also creates more victims willingly and knowingly. I don't really like him now.
Emperor: The more I think about the Emperor, the less I feel I understand. I don't feel like I have a real grasp on the Emperor as a character because there's so many strongly contradicting pieces of information. He shows exactly what he thinks he needs to get the job done, calls us his puppet...but is willing to part ways amicably?? He makes my head spin!
Karlach: I have to admit, what changed my opinion of her was someone else's take. If you think about it, her story is a metaphor for recovering after rape. I couldn't believe I failed to see the signs! It makes so much sense! The way my opinion of Karlach has changed is I want give her a much-deserved hug even more than I did before.
Lae'zel: She always felt the most "video game-y" of all the companions to me with her clear naivete and elitist personality we're definitely supposed to find offputting at first, but doing her romance on both her rebellion and loyalist arcs is amazing. As a rebel, her act 3 romance scene is so sweet, it could give a Hallmark movie diabetes. But the same scene on the loyalist path is hard to watch, it's so bitter. The way my opinion of Lae'zel has changed is that I feel I have a better grasp on just how strong the feelings she's been repressing are
Minsc: For the longest time, I enjoyed his silly idiot persona at face value. "Lol, what a dummy." Then I got to thinking, why am I ok with looking down at him for not thinking the way I do? Then I realized I felt the same way about him as fans of the Big Bang Theory or Resident Alien do about their characters, and I was ashamed for that failure of empathy. Minsc still makes me smile, but now I try more consciously not to fall into the trap of feeling like I'm somehow superior to him.
Minthara: My opinion of her honestly hasn't changed. Everything she believes and half of what she says is so utterly reprehensible and unhinged that I find it delightful. She's irredeemably evil, and all the better for it.
Shadowheart: I needed three playthroughs to understand her. Like Lae'zel, she felt very video game-y in that her secrecy felt like it was masking a sweet personality(the snarkiness helped though). My first failing was giving her parents what they wanted and letting them die. My second mistake was doing her evil path. It dawned on me in my third playthrough: her story is about being trans and the Sharrans are an analogue to conversion therapy. It's incredibly obvious if you keep her parents around, that entire camp scene is about her deadname(Jenevelle) and her remarkably understanding parents. Related tangent: I find it hilarious that one of the Sharran self-help books is about keeping people from touching themselves, and that controlling others' sexuality like that is textbook cult behavior.
Wyll: My first impression was actually that he was a bad guy pretending to be a superhero. His introduction gave me the impression he was quite sadistic, and that Blade of Frontiers thing seemed like a really shallow cover. After completing my first playthroughi my opinion of him has been consistent, though.
Gale, Halsin, and Jaheira: Completely static opinions. Gale is a techbro with loose morals, Halsin is prone to the naturalistc fallacy but is otherwise the most progressive and moral party member, Jaheira is a snarky crone, and I haven't seen a way to change these opinions aftera crapton of playtjroughs
