Have to say this book was pretty disappointing.
It felt like this wasn't a main book but some in-between novella. It's like I missed a book that was better written and had a big conflict in it, and this book was a little novella to accompany that to give you the perspective of other smaller characters during the main book.
(Like how there's a book called Elantris, and then Sanderson brought out The Hope of Elantris, a novelette of other characters perspectives' set during the main book, Elantris)

Except,

this

the main book??? 😵💀

I don't know how we went from such an action packed, gripping, and incredibly fast-paced book full of intriguing world progression, amazing magic discoveries, new characters that were great and interesting and actual conflict that feels like it was meant to happen and the clues were there and it had a purpose to the narrative. 
How'd we go from that...

So I'll start with one good thing of this book:
The improvements. I believe the interludes were done much better in this book, it felt like I understood things better. Great!

Now for the rest of the book.
The whole book felt anticlimactic, rushed, yet slower than the other books.

I have absolutely no idea why Eithen let Daisho use the Archstone at all, surely it would have been smarter to get him to reveal it in front of the head of the Skysworn? This is Eithen, of course he could have manipulated that into happening.
It would have done everything he wanted, shown they stole a forbidden artifact against the empire, shown he had murderous intend for simply possessing it, shown himself to be someone putting himself about his clan and the entire empire. He would have been shamed to bits.
It did not need to be used at all. This entire big event felt so engineered and forced and neutered. It literally felt like there was no stakes, nor was I even invested in anything, because it was so blatantly fabricated instead of a good build up and actual consequences happening and the enemies being scarier.

The entire big conflict event was shite.
Seriously. I felt zero stakes. It came out of nowhere, didn't feel necessary, and of course wrapped up off camera at the end while everyone huddled together hiding.
Lindon levelled up to high gold, nice...off camera! 😑
What I've loved about the series is that we get to see how Lindon and Yerin grow and level up and become more powerful, that really felt completely missing from this book.
The enemies were awful, they spawn from blood no matter how small? Awesome.
Executed well? Nope.

It really felt like the characters did nothing in this book; no progression, no advancement, unnecessary, stakeless, shoehorned-in conflict, wrapped up piss easily off-camera.

There was like 4 great and memorable scenes, and that's it.

Also Lindon losing his arm and gaining some rare unique experimental remnant arm was awesome, annnnd nothing really happened with it other than comedic use.

Yerin now

controls her evil passenger? Great.

Now it'd be interesting to see how she progresses in the next book.

Jai Long has fucked off with his sister and the book literally told us they'd never meet Lindon again, it literally said that, it didn't imply it, nor did it leave it to what-if, it straight up said it.

Eithen is still fun, but he just wasn't doing it for me this book.
The end scene was great,

loved the scene with Eithen showing the marble and his vision of Ozriel to the gang.

There's only one other thing I can say positively and it's that the fight with Jai Long and Lindon was really fun and gripping, articially drawn out and forced at times, but the action was well written and really stoked the fires of imagination.
It was still artifical af though. What was the point of curing Jai Long's sister in the previous book if he's still gotta fight him anyway, and why'd he take off his arm. And then the character fucks off forever.

This whole book was bullshit and frustrating and grating. It gets a 3 star from me because most of the action scenes were great and well written, and Eithen was still funny and I still love the main characters and I still love the world.
But that's me being generous.
Please dear fuck say the next book is better and returns to form!