Things I loved: The world! I could see every scene so clearly, and we get to travel from the awful prison/labor camp where we first meet Celaena to a kingdom with a sparkling castle built of glass. The history, the hints we get of magic still residing in places even though the king has done his best to stamp it out, and the lush castle setting juxtaposed against political intrigue and a competition between assassins is fabulous.
I also loved the competition between the assassins, though I wanted more detail on Celaena's skills. Maybe more examples so I could fear her kick-butt-ness instead of having to take everyone else's word for it. She came through in the end, though, and the last competition for the championship is a brutal, heart-wrenching scene worthy of ending this epic novel.
In addition, I was fascinated by the secondary characters. To be honest, I liked them better than I liked Celaena most of the time. I hope we get to see even more of them in subsequent novels because I think we've just scratched the surface on what they're capable of doing.
What Left Me Wanting More: As much as I was interested in the competition and the court intrigue, I wanted more from Celaena herself. Someone whose parents were murdered at a young age and who was raised to be an amazing assassin, who has the blood of countless people on her hands and was then tortured in a terrible prison for a year ... that girl should be traumatized. Nightmares or bouts of depression or fear or self-reflection. I had a hard time emotionally connecting with her because I'm not sure she's in touch with her own emotions. I also figured out the answer to the mystery (which is OMG WHAT??? crazy suspenseful) super early, and I would've liked to wonder a bit longer.
All in all, this is a great start to a new fantasy series. Fans of excellent world building and heroines with mad fighting skills will gobble it up!