I love Solastas UI. It is simple, intuitive, and functional. Not a fan of fancy buttons which take ages to read or find(I'm looking at you "sort inventory"). And I absolutly adore the visualisation of dice rolls.
About grid movement outside of combat. That because the whole game is basically a square grid. It may look less immersive, but it makes coding of pathfinding and targeting a lot easier. And we all know that in BG3 those are not even close to be finished.
About rules. I kinda made my peace with the fact that in BG3 5e was modified to the point where i barely recognize it. It's not bad on its own. Problem is that the little semblance of balance that existed in 5e, is gone. And now time that could be spent on ironing out bugs or adding new features, has to be spent on balancing the game from scratch.