Reading about the book you'll come across the word "grimdark". It's a subgenre of fantasy that Damien Walter, writing for The Guardian, sums up as "bigger swords, more fighting, bloodier blood, more fighting, axes, more fighting" (he's not a fan, can you tell?).
In the case of The Poppy War, Walter wouldn't be wrong. It's mostly war and fighting. It starts lighter, with a kind of Harry Potter-style school where the central character enrolls and learns shamanism (and fighting). Then school abruptly turns to war and the second half of the book is just fighting. It was definitely entertaining, I liked the worldbuilding with its East Asian influence, and I avidly listened through the audiobook. But beyond wanting to know what would happen next, I didn't really connect with any of the characters: too grim and too dark with a sort of disturbing justification of violence similar to Todd Phillips' Joker (which I loved by the way).
I wasn't amazed, but The Poppy War is the first book of a trilogy and it was entertaining enough to get me to read the others (at time of writing I'm already past halfway through the second book). If you like fantasy and dark dystopian fiction, you might like it too.