I think one area that needs to be nailed is roleplaying immersion. I tend to always play a good character with varying levels of lawful/lawlessness. Having as many dialogue options to address every situation as your character would is what Baldur's Gate 2, as well as Fallout 2, nailed, and made me feel like the Bhaalspawn and Chosen One were memorable characters with their own identity.
BG3 should allow options for all alignments to address situations appropriately. I think that's hardest with a good character, since players have a variety of things that they may or may not find morally objectionable. Though I think there should be options to be very manipulative and cruel for evil and chaotic players. Going off of Divinity Original Sin 2 all quests should have satisfying conclusions that have options for both good and evil characters - which was one thing that was most noticeable about that game in terms of flaws. I say that having a good character is harder for developers because if you're playing and fully immersed in your character being a paragon who always tries to protect innocents, if a quest just does not let you try and get a happy outcome without your character showing a reaction that makes sense then that breaks the immersion, and if that happens even once it can have a major effect on someones' enjoyment of the game even if the game excels in all other areas.
