Well, I'm resigned to the expectation that this game will have a similar crappy combat system as the D:OS games, even though Larian will strenuously deny that it is a copy of the D:OS system, but hopefully at least in a few other areas the game will be good. For example:
1) Keep party size at 6. I love these kinds of games precisely for my party of companions and all the interactions with them as well as being able to develop them through the game. So a reduced party size, by definition, is a direct reduction in my enjoyment. A corollary to this point: please give me a UI screen where I can simultaneously access the equipment of all of my companions, not just the ones currently in my party. I don't horde my best equipment just for the current active party members. I like to distribute my equipment as appropriate across all of my companions, and it is a serious pain to have to swap party members in and out of my party to distribute equipment.
2) Stay true to D&D and Forgotten Realms lore. The lore is WAY more important to me than the rules. I am a Forgotten Realms lore junkie. I own and have read almost all of the FR novels and FR 3.5e sourcebooks. A corollary to this point: spread the game around to other parts of the Realms beyond Baldur's Gate/Sword Coast. The setting has so many very interesting places in it. Let's go visit them already!
3) Environmental reactivity is well and good, just please not like in the D:OS games where in every battle water puddles and oil barrels and collapseable walls and such are always conveniently available and placed exactly how you want them.