Throne of Glass is a wonderful, fantasy book. I loved the hard edged character of Celeana, and most of the secondary characters are great to read.
If I had any issues, they would revolve around Celeana's complete non-killage policy, once she's outside. It's made clear that the King, is unpopular, a tyrant, and Celeana's enemy, yet she doesn't even consider killing him. There's no effort to plot his murder (which would solve several problems, and make sense for an assassin) and a lot of the book involves Celeana staring at herself in the mirror.
The competition is a reasonable part of the book, but is a little short-changed for the other, more YA aspects.
I did enjoy the book, and will be reading book 2, but I do wish that the author begins to show, Celeana's rock-hard nature, rather than just tell us what a good assassin she was.