As long as I can change the appearance then yes, I enjoy the system. I will definitely play through the game as Astarion sooner or later. Changing the appearance and having the ability to choose what I say is enough to make the character, well, me, so to say.
The system is really not so different from them being normal companions you have in many other rpgs, except you can choose to play them, I know people complain that the origin stories are cooler than the default character, and while that is true it is the same for other RPGs as well. Morrigan is much more interesting than my warden, Saverok/viconia/xzar(and so on) is more interesting than my bhaalspawn. I think a lot of these rpgs would have had similar complaints if you had been able to choose any of the companions to play as instead, just like you will be able to in bg3.
I would still really like to see an origin system like in Dragon age origins, that added quite a bit of flavor to the default characters but in a game with so many races and classes, it would not be an easy task.