As of now, the only resemblance between the two is the world it plays in. There are no remarks, notes or anything really related to any of the predecessors. So at this point in time the title Baldur's Gate 3 is misleading. It should instead be called: "A Forgotten Realms Role-playing Game", because this is the only connection, the setting.
Now this is likely subject to change, as we are in the first act with little interaction with the outside world or lore. There might have been a nod towards previous games, that I might have missed, but nothing that would bring back memories of olde.
As for the other things you mentioned: Depending on your knowledge on DoS games, 5e edition, D&D in general, as well as your own level of inquisitive mind, the game is either ridiculously challenging or extremely easy. It is not very accessible or transparent. Now BG 2 was worse, as it did not tell you a lot either, but I played it on Normal and Hard multiple times without ever using one skill other than spells (offensive spells mostly). I still have no idea what I did 20 years ago and every couple of years when I replayed it. I only learned in 2016 what 1d6 actually refers to and only in 2018 what Thac0 means.
This means I finished the games for the story, the gameplay was just icing on the cake and would have offered me a great experiences over and over, had I ever wanted that. BG 3's story, when compared to the first act of BG 2 is...unremarkable. Irenicus alone, makes for a great villain and entry to the story. The child of a god thing of BG1 was nothing new, but was decently presented. BG3 brings no villain and no new storyline, a parasite in the head is a common trope of stories. It is also decently presented, though, with a lot of cutscenes and a general tendency to visual storytelling over textual. However BG2 made me feel invested right from the start, although one could argue that at the age of 15, it was easier to impress me, although many other games still manage that. BG3 has not, so far.
The companions are, very special in BG3. So special that they overshadow the PC in how remarkable they are. They are also pretty edgy, so much that it makes me roll my eyes and I am remarkably uninvested and indifferent to any of them. This is not much different with the BG1 companions who often were just supposed to fill a role, but they had stories of their own that were rather relatable. In BG2 I had much more investment right from the start. Minsc and Jaheira I think never left my party at all. I always admired her and I thought Minsc was hilarious. I always romanced Aerie, but I hear the other romances were also satisfying. I loved all the banter and the amount of meaningful banter they had in between giving them more depth. Korgan and Aerie come to mind, two polar opposites, yet when Aerie breaks Korgan concedes that all he tried to do was make her fend for herself. Or Edwin in both parts. PoE characters also come to mind, they fit in the same role. Each had depth and character, yet many did not have an iconic background. They just were mercenaries, students, artists regular dudes with regular lives and relatable problems and also dire consequences.
BG 3 has interactions, and yeah some do not like each other, and maybe one of them leaves or dies or disapproves your action. I just do not care, though. It feels like a Telltale Game. If Minsc would advise me not to pick up the Sword of Superpower +6, I would have listened to him. I could not care less what Shadowheart thinks. Now this might also be, because of the first act and apparently you might not keep all origin characters, so they might be a bit like additional PCs more than actual companions, and the real guys are added in later acts. So that would explain the shallow, yet super special companions.
Gear-wise and possibility wise, the game seems great. I have seen players run with gear I have no idea where they got it from and there seems an awful lot of min-maxing to do, even within the first act. There also seems to be a lot of replayability since you seem to constantly lock yourself out of content, if you take certain routes and decisions.
From a gameplay mechanic point of view it seems alright with sheer endless potential. The UI and the general comfort is cumbersome to awful (e.g. party movement), but these things are also likely to be fine-tuned. There is a reason why the DoS games were so remarkably well-received. The full game will likely be a very good RPG.
If you are looking for a true successor to BG2 to bring back that feeling, because you like the story and the characters and the world, I would advise to not purchase or play yet. It will likely be disappointing if this is the main reason, like it was for me. If you are a DoS lover, that wants a fresh world go for it. If you are a D&D lover that is not bothered with some freedom taken from the ruleset, you will feel right at home.
