The story begins with a devastating scene that leaves our young protagonist scrambling to survive. Her survival is dependent on keeping her gender secret. Hello, Alanna (from an old favorite). There is plenty of action, and I love that Alex is a better fighter than the men in the book. She is so fierce.
There is also an obvious-- and sometimes annoying-- partial love triangle thing going on. She flitters between two main guys and it gets a bet irritating at time. Especially since one of the guys does an awful lot of pouting about it. Not very manly. She also doesn't seem to know which guy she prefers. At times, she was very wishy washy. I'm curious to see how the romance plays out in future books, but I have a feeling I already know. We shall see.
As for the writing, I think Defy was a great debut. The world building is very detailed. There are wizards and tons of secrets mixed in with a healthy dose of magic. If you're a fantasy lover, this will appeal to you.