Shadowheart's story is pretty stock, but I'm okay with that. She has drama, but it's in the expected range of drama for a fantasy character. Also, for all that she has main character drama for the people playing her as the main character, she's still reasonable in her attitudes on the boundaries of our relationship.
Astarion just comes off like a spoiled brat throwing a temper tantrum. I know he has trauma as well, and I'm usually fine exploring a vampire storyline, but he makes me a bit tired.
Wyll is a drama queen, out and out, and he is very selfish. He's very much about doing the "right thing" but loses the track when his personal issues cloud the situation.
Gale is a bit casually condescending and also fairly selfish, and he's not as upfront about "there's things I have that are not your business"... and when you're less up front about your issues than the Sharite....
Laezel is a stock githyanki, which means we're her subordinates, she expects us to do what she tells us to do and she's perfectly willing to sacrifice us in the name of her goals. I'm willing to explore her story to see if there's something interesting beyond that... but if Alfira and Karlach are on the companion list she's likely going to not make the cut for my first run through.
I'm hoping they allow for expanding the party size so that you can get more versatile party builds, but I'm cynical about that. 4-person parties seems to getting more standard on RPGs and games like this. Which is a bit sad because a CRPG can much more easily handle a 6-person than a TT GM can.
My hopes are on Alfira and Karlach too. I think, Karlach is a confirmed datamined companion and it is my hope, that Alfira will be another companion. Plus Halsin.
And yes, I would prefer a party of 6 over a party of 4. I think, it's ok with games liek Dragon Age, where you don't have as many classes, but in D&D you have so many different classes, that it is a shame to limit yourself to 4 characters. Plus I always have some characters in the party, because I like them, even if I might not need them, because my character already fills in their roles (Varric in DA2, Garrus in Mass Effect, Kivan in BG1, Mazzy in BG2...).