It was foreseeable after Fireborn that the worldbuilding would kind of fall apart at some point -- both metaphorically and literally speaking, I guess. The discrepencies I had picked up in the first book and started to get annoyed by in the second were only amplified in this one, much to my dismay. It made it impossible to enjoy the story at times, which is the reason it took me forever to get through this last installment.
Honestly, I think Skyborn should have been a standalone. A bit of a tweak to the ending would have made it satisfying despite the cliffhanger, or maybe book 2 and 3 could have been condensed into a single, more focused volume to make it a duology. Shadowborn has even more filler than Fireborn in my opinion, and I didn't care for most of it. Yes, the scenes flashing back in time to before the ascension explain how we got to where we are when we enter the world but they just dragged on and on for no reason, adding entirely one-dimensional and inconsequential characters to an already large roster of the same. The sidequest to sign the peace treaty with Candren gives us insight into at least one of the other island nations but ultimately, it was superficial and did little to contribute to the story or stakes. Truth be told, the fact that the twins literally got away with murder during that meeting broke most of what little interest I still had in those characters.
The more I read the more annoyed I became by the inconsistencies in worldbuilding. The size of the population, number of Seraphs (how were there still any left by the time we get to the climax, espcecially those from Elern, Candren and Sothren who, by the book's own description, got slaughtered by Center's knights earlier that same day?), distances, how much time it takes to get anywhere, as well as the number of prisms and how much charge they hold all seem to magically change depending on what the plot requires. I still have no idea how big these floating islands really are. Saul, who was at some point possibly one of the main characters, just straight up vanishes halfway through the book without explanation and gets one last line in the final battle before never being seen again. Liam's entire story arc was pretty pointless, as was the (second) invasion of Weshern, and just the simple act of Kael repeatedly cutting his hand with his sword during the climax, even though we learned he had handed both of them to his sister only a couple pages earlier, was just the last straw. I couldn't care less about most of the battle scenes or the pointless subplot in which Bree got framed for murder. By the time all was said and done, I had absolutely no concept of how much time had passed between the end of book one and the end of L'adim. Going by how none of the main characters is bothered by injuries acquired at several points throughout the story I assume they've had some downtime in between battles but it certainly doesn't sound like it when reading the book. For all I know, books 2 and 3 played out across maybe two weeks and they all have superhuman stamina on top of very high healing factors.
In my review for Skyborn I said I didn't care about the holes in the worldbuilding, and in that first book I think that is still the case. But by Shadowborn it read a lot as if the author made things up as he went along, which is a real shame. Mr Dalglish himself actually confirms this in his final author's note, with a challenging: admit it, some of [these things he made up on the spot] were cool. And sure, the rule of cool is absolutely valid -- who cares that the mechanism for flying makes no sense when you can have awesome aerial battles. But that kind of thinking only works if used in moderation.
All in all, I respect the author for experimenting with this story and to hell with what others think. It may not have worked for me but going by the overall rating, it has certainly worked for others. I did like Bree's final send-off and the somewhat open ending that leaves plenty of room for the reader's own imagination and the characters to live on. I just wish it had been planned through from the start.