Of course this is just opinion (and it’s been a long time since I played DOS:2) but what I noticed were mainly refinements (facial expressions, voice acting, graphics) and scope. There’s also the sheer amount of content variation in BG3 in that you can play a handful of times and see a lot of completely new reactions, dialogue, and quests depending on decisions and party composition. For instance just picking a Dark Urge character or not can make the game feel different.