Baldur's Gate and D&D are two different things. Temple of Elemental Evil had a much better implementation of true D&D combat than Baldur's Gate did but you wouldn't call it a better Baldur's Gate game.
Barring the fact the writing and tone of the game isn't actually as good as we remember it, it's still a fact that Baldur's Gate was as much about the adventure as it was a combat game, probably more so in the first one where 70% of the game was just an endless series of trash combat punctuated by a tough fight or two for every map you explored until you got to Baldur's Gate (of course, they were trying to replicate Fellowship of the Ring they had to keep it simple or it wouldn't have worked for that open world, exploratory part of the game).
But really, the point is that this doesn't look like Baldur's Gate 3. It looks like Original Sin 3 except now it's D&D. Maybe a best case scenario considering the alternatives but certainly not exactly a successful sequel to that game, not for any of us who remember what it was like when Baldur's Gate hit the market.
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I know exactly what you describe when you talk about the mystery of fantasy and wanting to relive it. It's like the difference between Tolkien's writing and Peter Jackson's movies.
I don't take issue with that, I just think decreeing the quality of the game at this stage, based off leaked screenshots of an unfinished product, is unwise.
And most of all, I don't think the combat being turn based has any bearing that or 'a sense of real adventure'.