My main and (almost) only complaint about this book is that it ends just about when it starts to get really good.
It starts a bit slow, and first few chapters feels like they were just backstory filler we needed to slog thru before the action starts in earnest. The frequent foreshadowing - and not very subtle, in some cases just stating things like "this is the last time he will see her again" - definitively contributed to this.
But then the alien Carryx arrive and it really takes of. One thing that stands out in hindsight is how this alien invasion avoids most of standard SF tropes. Reading this book felt a bit like when I read all those old (outdated even half an age ago) Golden Age of SF histories as a boy, when everything seemed fresh and wonderful. Except what happens to the humans invaded here isn't wonderful, it is horrible.
These aliens aren't Martians invading because they are jealous of our women/food/water - these aliens are a brutal colonialist empire just after grabbing planets to gather resources in their Endless War. This isn't a clash of civilisations - this is a gunboat showing up to a remote island, shelling the natives on first sight and kidnapping a boat load of them to see if the population is useful as slaves, or if they all should be exterminated. No hard feelings, just ice cold logic and calculations. The transport from Anjiin to the closest alien stronghold is reminiscent to the nightmarish transport on slaver ships, or the freight cars going to an extermination camp - except aliens at least attempts to keep most of their cargo alive. Freight across the stars is expensive after all.
On arrival the instruction is clear - be useful or die - but also frustratingly unclear, because the alien overlords doesn't care enough to understand their new slaves.
And this of course is mirrored in the captive humans own attitudes to their fellow slaves. Outside of Dafyd, none of the others even consider that the other species enslaved by the Carryx may have their own agendas or struggles. At least not until another group of alien slaves decides the humans are making too good progress on their tasks.
Hopefully this theme will be further explored in remainder of the trilogy. Because being human is to try to understand and have empathy.