I rather liked this story in all its remarkable understanding of beauty and all the shades of gray in life. Fire is a great deal more introspective than Graceling, which is understandable due to the differing natures of the heroines -- Fire's talents are more passive than Katsa's. With her sort of upbringing, it's understandable as well that she'd have quite a lot more to angst about, but her angst is forgivable, considering her history with her father, and she doesn't let it get in the way of what she has to do.
The reader may also rest assured that though her appearance is a specimen of physical perfection, she is a delightfully flawed character, and not at all superhuman, mind-bending abilities aside. Katsa's seeming infallibility (save for Leck's Grace) was the one thing that kept me from becoming fully absorbed by Graceling -- I loved her for it, but it did keep reminding the practical side of me that this isn't possible. Which is odd, because if you think about it, a person who can control other people's thoughts is less likely to occur in real life than an uncommonly hardy and durable one.
What I liked about Fire's abilities is that it was an excellent balance of harm and benefit, and that we get to see her developing it throughout the story. Said story is a bit slow, yes, but it adds to the bleak atmosphere that surrounds Fire in the beginning of the book. It livens up towards the middle and is brightened by a cast of supporting characters that I loved even more than Graceling's (though that is possibly because Po's family appeared only at the very end).