My two biggest complaints so far, especially considering that the game has Baldur's Gate in the title:
1. How do you look back at BG 1 and BG 2 with their glorious, beautiful, and immersive UIs and decide that what we got in this - functional, but stylistically sterile - is the vibe you wanted to give the player to say "yes, you're playing a Baldur's Gate game." They didn't even have to present it much differently functionally, just add some stylistic flare to it reminiscent of the predecessors. And that definitely carries into how items and books are presented. We go from those beautiful pencil sketches when you examined an item to a rotatable 3D model. And book presentation is atrocious compared to the originals. Some generic typed font slapped on top of a generic book texture, instead of the great font and letter-headers on top of a convincing parchment background. And don't even get me started on the contents of the books: bare-fucking-minimum attention given to them. Bringing these things into Baldur's Gate 3 would have gone a very long way to impart that original atmosphere into the game. Larian, fire your UI designers. They fucking suck ass. And whatever intern you've got writing the books.
2. Why does Larian hate portrait art so much? How can you look back at BG 1 and 2 and not see those portraits as a defining aesthetic contribution to the whole experience (even the BG2's were much worse than the first game's). Who looked at these still shots of the 3D models and thought "wow, that looks GREAT!"
So some niggling aesthetic things that I feel would have been very easy to remedy in order to pay tribute and do honor to your predecessors and their fans.