Graceling and Fire--Bitterblue has an ordinary human protagonist and takes places almost entirely inside a castle, it's still compelling.
Bitterblue follows Queen Bitterblue as she attempts to rule the kingdom of Monsea eight years after the death of her tyrannical father King Leck, who is killed at the end of Graceling. Though Bitterblue desires to be a good and just leader, the secrets left behind from Leck's reign continue to plague her people.
When the novel begins, Bitterblue is in a haze; though she's queen, she seems to have little control over or knowledge about her kingdom. As a reader, I also felt this haze, which is perhaps appropriate, but somewhat served to distance me from the book. About a hundred pages in I really felt like I needed to start the whole book over again (though I decided not to).
Bitterblue's own journey is jumpstarted by her decision to sneak out of the castle disguised as a commoner (ala Jasmine in Aladdin, making it seem somewhat trite). In the town, she meets two thieves, Teddy and Saf, whom she abruptly becomes friends with. Though those relationships are essential for Bitterblue's discovery that much of the truth about her kingdom has been hidden, I didn't believe the ease and suddenness of their friendships, and Bitterblue's later romance with Saf was far too obvious from the beginning.
Nonetheless, somewhere along the way I fell in love with the story. Perhaps the return of Kasta and Po (protagonists of Graceling) helped, as did the solid assurance of Lord Giddon. Maybe my desire to know the truth of what's happening it the castle and Leck's lasting effects kept me going. Regardless, even though relatively little happens, I started to read eagerly.
That truth, by the way, is far more horrible than can be imagined, and I almost wonder if the horror of it is treated a little too lightly. That level of atrocity, murder, and suicide somehow just didn't fit the book's style.
The romance between Bitterblue and Saf didn't do a lot for me and lacked the power of Katsa and Po's love (or even Fire and Brigan's). Nonetheless, I once again commend Cashore for having a unmarried young adult couple have safe and consensual sex, something I'd like to see more of.
It isn't necessary to have read Graceling or Fire to understand Bitterblue, though characters and events from both previous novels make significant appearances, and I rather wished I remember more from those books while reading. Nonetheless, despite my quibbles, I believe Cashore is one of the best young adult fantasy writers today, and I'll read anything else she writes immediately.