How are the characters/party members writing? Not too bad?
It's not like there's a whole lot about them in the first act. I definitely would prefer to see them interjecting MORE in dialogues.
But what's there is not half bad and I can definitely see them growing on me. They all seem to have a less obvious angle.
For instance I've seen a lot of people dismiss Shadowheart as "bitchy and angry". She's neither. She's a bit a guarded and on the "sassy" side of thing, but you can already see her warming a bit to you after few hours.
Lez'something (the grinch lady) is a ball of rage and pride at first. Like may of her race she's single minded about ONE goal and everything else is worthless in her eyes, but a wake up call is on the way.
Gale seems like the typical airhead blabbermouth scholar. You know, the chatty, awkward nerdy type that always says a line too much. At time hilarious, at time slightly annoying. But you quickly start to get the sense that there's a lot more he's not saying upfront.
Wyll (which turns out is not just called "Will" because his father couldn't spell properly) is a likeable wannabe hero that always inflates the tales of his past achievements. He too will shortly turn out to have a big secret he's trying to hide from the parrty.
Astarion is a Dorian Grey/Lestat wannabe that at least so far seems to just love flaunting his sadism, his sexual degeneracy and his overall smugness. My least favorite so far as an archetype but I can't exclude a good arc ahead, yet.
What is impressing me on the other hand is a lot of random NPCs you cross in your questing around. There are plenty that are wonderfully expressive in facial features, gestures and voice acting and their writing seems to be pretty goddamn solid.
Auntie Ethiel comes immediately to mind, but she's not alone.
Nostalgia is a hell of a drug, but if people were a bit more honest about it you'd hear around more admission that some of these characters in BG3 are already topping by a wide margin most of the performances in the old BG1 and 2 (which to be honest were never anything special, anyway).