This and how the 5e rules are adapted are my two main reasons I'm only cautiously optimistic for BG3 and not outright excited.
I have every confidence in Larian's technical design capabilities, meaning that however they implement things, it will be done well. Perhaps not to my tastes, but solid and well done. I'd like to see them adapt 5e in a similar fashion that BG1/2 adapted 2e. That's vague and hard to define, granted, but that's the best I can manage in describing it. I'm not looking for a 1:1 adaptation of the rules, but something that actually feels like it's adapting the 5e rules (and not just slapping D&D names and terms on a ruleset that has no connection to it at all...for an example of that, see Sword Coast Legends).
The main concern is the narrative for me. Again, Larian are good at what they do...but they have done nothing (to this point) to suggest BG3 won't be a parade of parody, satire and a constant tongue-in-cheek approach to the narrative. Even their publicity vid had Swen Vincke being his adorably goofball self (which I appreciate for what it is too). Do I expect grimdark like, say, Witcher 3? Hell no, and yeah, BG definitely has room for some goofballery (just as the previous games had)...but Larian has not demonstrated (yet) they can balance the silly with the serious.
