And to be clear, I'm not one of those who hates all the writing in the game, I've always maintained that it's merely uneven and that it does have some good bits, even some very good bits.
Same opinion for me, which is why the bad part stands out even more. It doesn't help that (except Sosiel) most of the bad characters show up as early as the Prologue so the worse parts of the writing are generally part of your first impression.
More thoughts about the different companions arc I've completed :
Lann : Classic. Been there done that, but nicely done, tied with the overall narrative, give closure to the plot threads started in the Prologue. Tropes and stereotypes aren't really an issue when they're done well. The dependable sidekick being an old guy well past his prime (with mongrel lifespan Lann is in his twilight years) is a nice idea, and they don't try to overdo it. Heard his romance is terrible and the scene with his mother sure was cringy, but romances usually are in general. Mostly give sensible advices on the council. Not really a lot of reactivity. Basically you make him believe in himself and he lives, or you don't and he sacrifices himself.
Woljif : Classic and stereotypical but I liked his dialogue. Sure gave a lot more Planescape-vibe than Arueshalae. Good depiction of what a realistic Chaotic Neutral thief would be. Wasn't surprised to see him run off and do his own thing when shit hits the fan and the camp is attacked. You can call him out on his bullshit and not take him back. Didn't go the Demon Woljif part so I don't know if there are actual gameplay consequences to it, but some C/C in his quest.
Greybor : How is this guy not Neutral Evil ? If Regill is Lawful Evil, Greybor surely is Neutral Evil. Deals with demons on regular basis, kills for money and doesn't have any qualm about it. Only it for himself, will betray you if you refuse to pay him etc. Neutral Evil doesn't always mean cannibal murderer or undead scythe-wielding elven cultist. Didn't find his journey and "dilemna" with the assassin guild really interesting. Wasn't really moved by the double-double crossing at the end. I guess you don't have enough interaction to build a believable relation of mutual respect with him. Like he said "you are my boss, I trust you etc" but I didn't really got the feel I worked to earn his respect.
Regill : One of the strongest companion narratively, lots of dialogue reacting to the majority of your decision in the game, very good in council, and an overall coherent characterization without weak points. But his personal quests were rather bland and the Hellknights were featured prominently in Act 2 but quickly lost the spotlight in the following acts. Wasn't really engaged by the pseudo-trial. Also his depiction ingame isn't really Lawful Evil. He's solely dedicated to his cause and not in it for himself, basically everything he does is rationalized in light of the fight against demons. His most heinous action is in his character intro (murdering his own wounded soldiers) and it is quickly shown as entirely justified by the circumstances (most of the captives are turned into ghouls anyway). He is more of a very gray and ruthless Lawful Neutral than a Lawful Evil.
Daeran : Good on paper, so-so in execution. A lot of his jokes and quips aren't really well-written and fall flat. Not a bumbling buffoon but not an excellent comic relief neither. His personal quest is good even if a bit far from the main plot and tone of the game (cosmic horror). His interaction with Galfrey were amusing tho. Really a hit-or-miss character. Also he is neutral evil (because what ? He's rude and selfish ?) while murderer-for-hire Greybor is True Neutral.
Nenio : Very bad comic relief, no relevance whatsoever to the overall narrative or meaningful interactions with the rest of the party. One of the strongest character mechanically as she is a pure wizard with good stats, but you're basically better of with a mercenary for all the narrative value she brings (which is none). At her best she is inane and insignificant, at her worse she is unsufferable and pure cringe. Her quest is a massive puzzle slog.
Sosiel : Started boring, quickly turned bad and embarrassing. The sliver of character depth shown in his first mission (the faggy and artsy cleric being a violent and brutal man) was swept under the rug and forgotten. His drama about the perception of his brother felt forced and wasn't engaging. Like yeah he had a change of heart and went from one military order to another, why are we supposed to care ? Doesn't help that his brother, who is hyped during the whole arc as an interesting and conflicting figure, is really bland when you finally met him. None of the questions raised by his journey are answered and he basically has the same dialogue as the Lich graveguards.
Arueshalae and Ember are full-on anime and waifu bait. I fully expected it before even recruiting them but it fails hard with Arueshalae.
Her characterization is boring. She is already redeemed when you meet her, but the redeeming isn't her own, she was litterally brainwashed by a godess to erase her mind and imprint a new personality on her. None of her character arc shows any agency and meaningful dilemna. Yes you can make her fail her redemption by being a dick to her but it felt like an afterthought and not really developped. We don't really see her struggle with her succubus nature, her arc lacks severely in "Show don't tell". Also she is whiny and angsty everytime and not a really compelling person. Her interactions with the other demons help give more depths to the Act 3 and Act 4, but as her own character she's pretty weak.
Ember quest is nice on the C/C and reactivity and offers meaningful gameplay and story consequences but I wasn't convinced by the execution of the dialogue. Felt a bit mary sue while don't really giving meaningful insights on anything. Trying to write religious/philosophical characters is hard, and I don't think Owlcat succeeded in its endeavour with her. The Nocticula part of her arc felt a lot forced, but I read its (Nocticula "redemption" that is) directly from OG-Pathfinder.
Currently going through Wenduag and Camellia arc on my actual run, definetely finds them to be part of the stronger characters of the cast and I'm curious to see where will their journey leads.