Since you drag BG 2 for comparison - you could have your own child in that game, how's that for an rpg (granted, it was in the ending credits, but still)? I liked that scene you mention, arriving at Gilded Vale, it could have gone the wrong way and be laughable cliche about crazy, opressive lord of the land; but they managed to make it working.
Also, this whole Lord of the Barren Land quest line has some nice reactivity in the world - people have additional lines of dialogue when you help make a change on the throne, even those public heralds (Criers?) in Defiance Bay mention that fact. Quality of writing aside, that is a nice detail and got me more interested in how I handle quests.
And that's the only quest that has barely any reactivity toward your choices ,and even this is one is barren when it comes to details (Like you said ,if you change the ruler(kill Roderic) ,the tree gets picked up clean and the peasants are happier ,ladi fucking da.That's not nice reactivity ,that's just fluffy stuff that has no real repercussion, like getting a quest after finishing it or someone mentioning in a quest that would deviate from it's roots)This is nice reactivity ,no bullshit stuff like that,so please stop lowering your standards guys and see it for what it is,a mediocre game.
I played the game for 40-45h and ''Lord of the Barren Land'' is the only ''big quest'' that you could solve in multiple ways and having like 3 different outcomes that changes something ,besides a few lines from the peasants.The rest of the game is barren when it comes to reactivity ,even after the end of Act 2,everyone acts like the incident never happened,almost no one mentioned what happened to the duke or the other leaders.
Sad day for reactivity.