*cries eternally*
This was soooooo good!

Okay something that I need to get off my chest immediately is that I'm tired of seeing people in this review section saying this is just another Midnight Sun or Ballad of Snakes and Songbirds (idk if that is even the correct title) because this is not like those books at all. I've never been given the impression that Cashore is writing this continuation as a means for more money because each book has only added to the lore in a bigger and better form. She's also used her novels numerous times to start conversations in the YA community about issues like feminism, environmentalism (happens in Winterkeep), etc. I'm not going to linger on this anymore because I'm going to switch to my mix of pure, obsessed fangirl and analyst, but this is a note to all those annoying haters.

To start Winterkeep takes place five years after Bitterblue. I know a lot of YA people are not big fans of the books after Graceling because they start to have a slower pace, hold more adult themes, etc. and to that I say they sure do.
It makes them MONUMENTALLY better.
I would highly compare Winterkeep to Bitterblue because Cashore is expanding this world to new lengths I could never have forseen before. It also takes some time for the intense action sequences to happen, but it is well worth it. Just because the action isn’t as forthcoming as it is in Graceling or even Fire does not mean this book isn’t incredible. It’s very political to be honest. Lots of sneaking and scheming.
Lovisa, our newest character recruit, is a morally ambiguous teen, at times, who is torn on her allegiances and duty to her home Winterkeep or her to loved ones. Bitterblue, on the other hand, is just trying to protect and run her kingdom while dealing with another continent with insane technological advances (when compared to the Seven Kingdoms, the Dells, and their continent overall). When Bitterblue and crew start to see some mysterious and deadly circumstances taking place, they plan to get to the bottom of it.
Winterkeep is another piece of growth for this world. I laughed. I cried. And I most certainly screamed my head off. There's so many emotions that coil and boil throughout this story from the entire range of characters. I liked this installment specifically because a lot of the side characters in Bitterblue come farther into the light. Enigmas like Hava become invaluable to the storyline, and I've always been curious about her character after finding out her backstory towards the end of Bitterblue.
Now I cannot say much else because then I'd spoil you all, and that would be horrific because this is an amazing book. What I can say indefinitely is that I went through Winterkeep so quickly that it did not even feel like a 500+ page novel. I'm devouring the lore left and right and just trying to keep up with these marvelous foxes. Ooops I've said too much.. *wink wink*
Anyway, this book was incredible, and I know I've said this multiple times already, but I just need to say it again. Cashore steps beyond the bounds of YA to bring in environmental issues to the Graceling-verse and even a darker element to politics than ever seen before. She's always been an author even before the 2010's that discussed topics not yet mainstream, but she uses her fantasy books as activist messages essentially. It's brilliant and valuable.
P.S. As a little aside, they’re some changes to this story than what happened in Bitterblue. Keep the 5 years in mind because of course nothing is the same as it once was. People growth, mature, etc.

Just like without Cashore's previous books they're some heavy triggers, and I'm going to list as many as I can recall.
TW: Animal abuse, child abuse, gaslighting (mostly parental), prisoner starvation, near drowning, sexual assault (not rape but specifically rough, cruel sexual touching without permission), suicidal thoughts, kidnapping, claustrophobia, environmental cruelty/ deterioration, and bomb warfare.