I think that you're being a little too harsh. I didn't play the previous Baldur’s Gate games so I can't comment on that, although since it only act 1, there might be something later in the story that will tie it to the previous games.
The characters - at least those I played with - are interesting. I like that they don't agree to tell you their whole life story immediately. You find little by little, by small things you notice over time. Some of the information might only be available if you chose a specific race, found a specific object, made love to the character, succeeded in a persuasion roll, or made decisions that the character approves. It's the same as in a real dnd game: all the characters have plot hooks that are interesting and tie them to the plot, but the main story revolves around a different common goal.
I agree that enriching the background stories will make the story better, but they are pretty good now too, especially Astarion's. I think that his story is the most prominent one. Shadowheart's story, on the other hand, is a lot subtler and you can miss it if you don't find the correct items and succeed in the checks. I think that there should be things about her that we will find out no matter what we roll or find. That said, we're only in early access so there might be more character development we aren't aware of.
Bugs aside, I like the mechanics. It's fun for me to try and sneak to high places or behind enemies to get the drop on them and get a bonus from being on higher ground. There are some things that I would change or add to, but overall it's great.
