At 500 pages, the third book of The Sundering series, The Adversary, is thicker than the usual Forgotten Realms novel. Maybe it had the same deal as The Godborn of having a longer plot stuffed into a single book. I could not find any information indicating that, though.
I am not entirely sure to whom book title refers. I assume it is Asmodeus, even though the then-archdevil-now-lesser-deity is not directly present in the story. But it would make sense. In the novel, the warlock tiefling sister, Farideh, also plays with Wroth cards that include cards named same as the titles of the Sundering books. However, the cards (at least their names) were evidently a new invention, and the books were not named after the card game. That would have been neat.
The Adversary does not have any world-shaping events. I think the most relevant thing realmslore-wise in the story was how gods have in fact given different powers to people as the Shadovar suspected. A person deso not apparently even have to be a god's follower to become chosen. (Not to be confused the greater Chosen like Elminster.) For what purpose the gods are doing this, remains a mystery but it reminds me a bit of the Heroes tv show.
I liked how the story takes place mostly in the Lost Peaks where the Fountains of Memory – now in ruins – are located. I have lead a D&D campaign that visited the fountains and it seems blowing up the place was not that far from canon.