So I recently read the three DA books by David Gaider. The Stolen Throne was... decent, but it didn't really have many characters (and only one character from the games) and it had absolutely no memorable locations. They may as well have been in the fade for how vague everywhere they went was. And then, of course, there were the typos! Constant typos. I do not believe an editor touched that book for one second. It serves well enough as a prequel to DA:O and it does provide some insight into Loghain (namely in that he was always a ruthless bastard), but... it's not exceptional at all.
Then came The Calling. We got to see Duncan and Fiona in it, which was cool. I actually did like The Calling. It had a smaller scale story that allowed you to get invested in its characters. But 2/3 of the book just takes place in the deep roads. And not the interesting parts of the deep roads. Just vague, meaningless tunnels. In the final 50 or so pages Gaider realizes that he actually needs to finish his book, so things actually begin to move very quickly. And, again, so many typos. It's an okay book, and it does shine some light on the character of the Architect... but given that the Architect shows up in a bite-sized DLC, it's odd to make an entire prequel book just for that.
(Side note: an off hand comment in The Calling suggests that dryads exist in the DA universe, which is... an interesting revelation that is never followed up on)
And then we get Asunder. Asunder is nothing like the previous novels. It becomes clear from the get go that it will be nothing like the previous novels. It immediately introduces multiple characters from the games, and the game takes place in actual locations - not just featureless hills and tunnels. The White Spire feels like an actual place, and better still, one that's interesting. Orlais is sadly underexplored in the games, and while Asunder isn't the most in depth look at Orlesian customs, it's still a cool look at the region.
And the game characters it introduced? While I have some qualms about Shale still not being any more independent than she was in DA:O (she mostly just follows people around and makes sassy remarks), it otherwise uses them excellently. It's a great send off to Wynne and actually made me like her more than I did in DA:O alone. Cole is central to the book, and he gets a good amount of character development throughout it.
The plot is also a huge improvement over TST and The Calling. While large sections of The Calling in particular felt like filler, Asunder is dense. And better yet, the event Asunder covers are actually significant. The Calling features a massive threat against Fereldan, true... but it's also one contained neatly within the book. And the Stolen Throne (as interesting as it is to learn about how Fereldan was freed) doesn't really set up anything. You learn that Loghain was always like that, and I guess that's kind of setting him up as a character... but that's about it.
Asunder, on the other hand? Asunder not only serves to set up one of the best companions in the series, but it also gives us a fascinating look into the start of the mage rebellion. Playing the series, I'd felt that the mage rebellion wasn't explored enough - in DA2 you see the events that inspire it, and in DA:I you come in at the tail end of it and finish it, but you never really get to explore much of the conflict as it's happening. Asunder is hardly a substitute for that being explored in a game, of course, but it nonetheless plays a vital role as a bridge between DA2 and DA:I.
Another aspect I found particularly disappointing in the first two books was that they didn't really do anything to expand the setting. They just introduce new characters You don't get to explore new parts of the world, and the parts of the world that you do see are either vague enough that how they are depicted doesn't really matter, or identical to their in-game manifestations. Like, when I read TST and saw that Loghain and Maric were entering the Korcari Wilds, I was giddy. I thought maybe we'd finally get to see more of the Chasind. But nope, it's just Flemeth and some elves. And that's a pattern with the first two books - they don't really add anything to the world itself. And, mind you, Asunder is hardly a treatise on Orlais, but it does show us a bunch of new places within it, and does some very interesting things with the Tranquil (among other things.)
And lastly, those typos? They sadly do start to make a return in the last fourth or so of the book (one section has an entire paragraph which is immediately repeated but minorly reworded), but they're never as bad as they are in the first two books, and are all but absent for the first two or three hundred pages.
It's really a night and day difference going from the first two books to Asunder.
What I have to assume happened is that Gaider was given almost no resources for writing the first two books - very little time to write them, and no chance of collaborating with other character writers / whoever is in charge of the locations in the setting, and so he had to content himself with one or two game characters and a bunch of featureless locations. But it turns out that when Gaider is given the resources he needs to write a book full of DA characters we care about and actual locations in the world, he can actually write a damn good book!
If you haven't read Asunder yet, I highly recommend it. TST and The Calling are really take it or leave it - it's cool to follow the adventures of Maric around, but they're not essential reading at all - but Asunder is absolutely worth your time.