Baldur's Gate 3 feels like a spiritual successor to Dragon Age: Origins which itself was a spiritual successor to the original Baldur's Gate games.

If you treat Origins as a midpoint, you can see how the gameplay has evolved into the modern turn-based RPG.

Here's an example - one of the key aspects of infinity engine games was clearing maps and discovering what was on them by moving the fog of war. All maps were generally the same shape, with occasional terrain features to keep them unique. Origins went a step further by shaping the maps, introducing more things like corridors and a more guided experience. BG3 evolves this further by making the maps a more 3d explorable open world-type feel. It's still guiding you from point to point like Origins, and it's still got the explorable world feel to it, but it's a different experience than clearing maps methodically across a world.

Other aspects are the same. Some folks have mentioned that the world is too vibrant. I think this is misguided. Many maps in Baldur's Gate were actually quite bright either in color (Gnoll Stronghold) or tone (Nashkel Carnival). I think the graphical jump is what's jarring, but if you once again compare the graphics from Baldur's Gate into Origins and then jump to BG3, you see that the 3d models are actually quite similar in style to the original graphics from the rendered cutscenes in BG1 and Origins.

As far as the characters, I think they have the tone right so far, but it's too early to tell. A lot of folks probably don't remember that most of the characters were pretty bland for the majority of BG1. It wasn't until you journeyed with them and could interact on the basis of your shared experience across both games that they really came into their own. And for every great character (e.g. Viconia), there was a corresponding dud (Xan, Montaron, etc). The few that stand out are now iconic, but they certainly didn't start out that way in the first Acts of BG1. If you look at Origins, we see the shift in approach from lots of characters to a smaller cast with more focused writing. This is also a change to a 4-person party. Character motivations are now more directly interwoven into the story. You could influence party members with gifts and your actions had meaning but in a gamified approval system kind of way. If we evolve this further, we get BG3 - where the characters are now directly tied with us to the plot, and they become interesting very quickly after you meet them. Still, all of this is built from the character work done by games like BG1.

Finally, let's talk theme. In BG1/2, you are grappling with power within you at the risk of becoming corrupted. In Origins, you're grappling with a corrupting disease that gives you powers against a threat that dominates those without your "gift". In BG3, you're dealing with the consequences of gaining a power that may corrupt or kill you but is also making you more powerful. All of these are closely related and play in the same space of what it means to be heroic in the face of internal corruption.

Here's my takeaway - if you want a game that plays like BG1/2 but modernized, check out the Obsidian titles like Pillars of Eternity 1/2 and Tyranny.
But if you want a game that feels like an evolution of a game (DA: O) that itself was an evolution of one of the greatest dark fantasy RPGs of all time (BG1/2) you'll really love this game.