Does anyone here who has played the EA version thoroughly can make a statement how BG3's story is going to shape up? Are the themes mature and thoughtful, or is it all just another fantasy theme park? Can it measure up to BG2's Chapter 2, or least have a sense that it might?
I don't know if it can really be compared to BG2. BG2 had a lot of concepts underpinning it that weren't spelled out to the player explicitly. This is, frankly, a style of writing you just don't see often anymore. Especially not in games.
It's extremely reactive and the characters and their motives are, for the most part, believable. The dialog is decently written and the themes are 'mature', in that there is sex, violence and death, but I can't say I think any of the writers has a PHD.
It's fairly straightforward often times. I don't think there's anything of philosophy or nuance in this that isn't going to be explained at some point during the game. The best you get are temporary mysteries. E.g., what are the mindflayer worms in your head really? Who is Shadowheart? What is the person in your dreams? Who is 'The Absolute'?
If you watch the latest trailer on one of the bad guys, he basically just dumps his backstory in a cutscene. Did Irenicus do this? No. From the very beginning, he was a puzzle to be solved. And if you didn't pay attention along the way, you probably wouldn't even get who he was other than 'some elf who wanted revenge'.
I'd call BG3 a fantasy theme park, but an enjoyable and unique one, with some mysteries and cool things to do. But still a theme park.