In ME people I know often choose an answer not because it fitted Shepards personality, but they wanted the approval of their companions, so Shepard stayed a blank and didn't became a fully realised character.
Shepard didn't stay blank at all. What you seem to miss is that a party RPG is much about group dynamics, just like in real life. It's a typical reasoning in such situations to think about what the group or friends would do and how you could get their approval. If you act against the will of your friends, it's as much a deliberate decision than acting for the goodwill of your friends. I'd say this group dynamic is even essential for all group/party based RPGs and a defining difference to solo RPGs in which you only take the role of one character. In such games there is one element less to think about, specifically what your friends might think about you. It's a typical lone ranger approach. In a group RPG instead everything you do is a group approach, often with you at the center but with your friends/companions being essential parts of the adventure. You need them and often you want them to stay with you. That's actual roleplaying here and there and actually the opposite of a blank character. It makes some decisions even harder if you have to weight your own convictions and opinion on a topic against what might be the direct social consequence for your own character. Of course that element gets the stronger the better and deeper the respective consequences are. That's actually the reason why I hate the idea that your companions in DOS only tell you what they think, while they won't do anything beyond that no matter what. Sure, ME did the same and it wasn't perfect, no question. But DOS should build upon that and in no way cut back some of the most important narrative elements of a party based RPG...
In Original Sin I know now, that my righteous and law-abiding Knight is a vegetarian (because it would be cruel to eat somebody you can talk with) and that he is without fear and that my female Wizard isn't above stealing for the greater good, while being suspicious because the game rewarded me for their decisions.
There is not a single narrative reward for actions in DOS imo, especially not in respect to companions or your 2nd character. Simply because they don't have any real relationship at all beyond the situative minigame. Whether they are righteous or not makes no different for the interaction and relationship between character on a greater level which makes the system a lot worse than the one in typical Bioware games. It's just mathematics pressed into a number, ripped of any emotional impact. Of course much is imo a consequence of the game being made for co-op, where the core of the experience is the interaction with real players OUTSIDE the game. Such a systemic approach is perfect for that because it's main goal is not immersion and emotions based on character interactions but situative fun while you interact with your pals in real life.
So the system worked in SP, although I would have liked some more automatism during conversation. But if they balance this out in the sequel, this could work even better.
The system don't worked very well in SP altogether imo. It worked great for MP but surely not for SP. The main problem of narrative in DOS is that it's almost exclusively seen from a systemical point of view. Everything in DOS is based on systems, and so is the narrative and especially the interactions with characters inside the game. It's indeed mimicing the functionality and feature set of a PnP while pretty much disregarding the aspect that people play SP RPGs often for very different reasons. That's why the love&hate stretch goals is so incredibly important for the SP aspect of DOS. Done in the right way, it could enhance the systemic approach of DOS with the emotional impact it deserves for the SP. Relationships between realistic and lifelike characters (that are MORE than values on a character screen) and a narrative that forces the player to make moral, emotional and multi-layered choices with consequences that enhance the immersion and impact of the choices are what SP RPGs are imo all about, beyond the combat aspect for course (which is pretty much the same for both MP and SP).
About "one PC + companions" vs. "4 PCs":
I don't agree at all that Larian will go for a traditional implementation for the former (think Bioware games), but Swen already communicated that the latter will be possible. But seriously, I don't know how both are supposed to work in the same "mode", in the same campaign, in the same narrative. They are different on many layers and one will always limit the other one in certain aspects (like already present in DOS btw). It's imo not true that both ways are easily and simultaneously doable for DOS 2, especially not if Larian will enable MP hop-in/hop-off even if you want to play the game completely in SP (I don't speak about the option to turn your visibility on the lobby off). A traditional SP party RPG with lifelike and realistically written companions will always suffer from that approach. So I'm happy for all of you who basically want to play a PnP session with yourself ("4 PCs") because that will be possible in DOS 2, according to Swen and based on how DOS worked. The real issue here is though that many people who expect a traditional SP party RPG will be severly disappointed, especially after Larian announced that the want to improve on the narrative that much...