I'm going to be a dissenting voice here. I LIKE the idea of creating a single character and having other, fixed companions with their own points of view and reactions. I am not interested in role-playing versus myself - I wasn't in D:OS 1, so much so that I didn't play D:OS 1 on release - I waited until the AI personalities were added before playing for the first time.
I do not mind that I won't have the opportunity to customize my entire party, and that they will have their own distinct roles and strengths. It just means that I can focus on tailoring MY character in a specific way.
However, I'm a bit less certain on the AI companions never leave or attack. That really depends a lot on the specifics, though, and I have no idea what those are yet. It could be good, it could be bad. I don't want to be forced to take a spy for the Divine Magisters with us in our party, but other than that, it probably doesn't matter so much.
I was hoping we'd have pre-set companions, so you definitely aren't the single dissenting voice :p Role-playing all 4 characters yourself is basically schizophrenia.
If they don't leave, no matter what kind of atrocities we commit (if they are goody two-shoes), they are either woven from the same cloth as KotOR2's companions where they were all basically neutral, though it had a story reason behind it that I'm not gonna spoil. Suffice it to say it worked great. OR their personalities aren't strong enough to stand up to the PC (it depends on their overall personality if that is good or bad). It really depends on the context, simply put.