This book was at it's best when the author was spinning out her angel mythology. One of the things she did absolutely right was the world-building. She doesn't over explain; she just drops the reader into the middle of the world and leaves you to catch up. It's a great effect which makes the world feel more real. There's still some exposition of course, but it neatly dodges most of the giant blocks of exposition monologue you often see in first-person fantasy fiction.
That said, heroine Penryn is a little too good to be true at times, and has lots of convenient skills right when she needs them. Her mother pops in and out of the story when it's convenient also. The weakest parts of the book for me were the 'tender moments', trying to setup for Penryn's inevitable romance with Raffe. It felt more like a teenage girl crushing on a much older man who isn't interested, and she is reading too much into his gestures.
I think this series has a lot of potential to become more interesting. I just wish it wasn't so obvious the author was heading for the Penryn/Raffe romance.