Short version:
I'm devastated to report that this was not good. Sure, a lot happens, but none of it seems to mean anything. Every obstacle is solved with the same solution, over and over and over. Any statements almost made are accidental. After how much I loved the first one, I'm very disappointed.
4.5/10
Long version:
Maybe it's just me. I've read like, twenty of this author's books, and so his writing style is rapidly wearing thin for me. I used to find it all very exciting, but now it all seems so meaningless. I thought a new fantasy series was just the thing to get away from the Michael Bay vibes of all the guns and technology and explosions and action for action's sake. Unfortunately, the series can't get by on novelty alone.
I just figured out why I keep thinking "this 600+ pages could have been an email": There is no discernible emotional arc. There was for sure an arc in the first one; it was a coming-of-age story in which a young disabled girl rises above her peers and embarks on a dangerous quest for truth. It was fun to see Nyx gain confidence and find her voice. This second installment has... well, to be fair it has her budding sexuality going for it. But there's nothing for her to really struggle internally against, it's mostly go here, avoid danger, defeat this, go there. A lot of the core relationships are already established, so they don't do much developing.
I think this also suffers from too many characters. I like being able to check in with different people in different places all over the world, no complaints there. What I mean is there are often too many characters in one place. Good lord, there are so many long conversations where like six or seven different people chime in, and there are still more characters who are there and apparently just standing still in the background, doing nothing. Even action sequences have an objectionable amount of dialogue because we have to hear from everyone. And splitting the party doesn't help this problem, because we have to catch everyone up to speed when they get back together. I was there for that part! The characters may need a recap but I don't. What I do feel I need a recap for is who the hell are all these people. I can't remember that many names, and so when something dramatic happens to Jormathan (name I made up) who's been in the background this whole time, I don't feel emotionally connected to it because I don't remember who that is, what they've done, and who cares about them & why. Maybe that's intentional; maybe the overwhelming number of characters are just redshirted cannon-fodder for future installments. That's so disappointing. That's creating an entire person just to be a waste of my time to get to know.
To address my main complaint in the short version, I will have to get into minor and unspecific spoiler territory, be aware. What annoys me is, the author has given his character a proverbial hammer, and has made every problem that arises in this story a nail. Obstacles get defeated so easily with no downsides. This does the cliche anime thing where they're like "Oh no, Character has used all their energy and doesn't have any left!" but then the power of friendship gives them the strength to do one last thing. Quite literally. We are told in no uncertain terms that the characters' magic is completely used up, in its entirety, and to use any more would actually literally kill them. They go on to use that same amount of energy four more times in a row and I'm not kidding. And then later they go somewhere else and use a life-draining amount of energy again a couple more times just for good measure. It completely ruins the impact of their "sacrifice" because it's not even hard to save them. What was the point, then? I mean it's cool that they're supposedly willing to die for the cause, but that seems kind of cheap when it doesn't put them in any actual danger because another character decided it shouldn't. No clever skirting of the rules, no dramatic rescue, no finding another way. Reminds me of an asshole kid claiming that actually, he has a laser that can melt through all shields and a shield that blocks all shield-melting lasers.
Conclusion:
I can only hope that these problems are just second-in-the-trilogy syndrome. I have no reason to believe this is a trilogy rather than an ongoing series, but it definitely has a clear overall problem that has to be resolved sooner or later. It would absolutely suck to try to continue past that point with no ending in mind. So assuming that there is a planned outline for a finite number of books, most likely the last one will have more meaning, better emotional beats, a firmer grasp on its own rules, a satisfying conclusion, and, frankly... fewer characters.
The only question is, do I feel betrayed enough by this one to not bother getting there? Time will tell.