I brought and read this book a little while back, so bear with me if comments are a little vague.
The main character was smart, sassy, not overwhelmingly beautiful, and easy to get on with.
The magician guy who first saw her powers from the Guild is really well-written too (can't remember name).
In all, this lady author has a talent for writing good characters and snappy dialogue.
The initial part of the book I found quite good, although the chasing around carried on a bit too long. The whole Thieves set-up is a little cliched and nothing you won't have read before, if you've tried Feist.
Once she reaches the Guild, it becomes a little Harry Potter/Tamora Pierce-esque. By that I mean, she makes enemies and starts learning a little magic.
Once the plot kicks in featuring the High Lord, things definitely pick up.
All in all, my verdict is a fairly decent fantasy novel, with potential to get really good in the next two instalments. Some of it is pretty cliched but this is kinda to be expected when you handle magic as a main topic.