In Arrows of the Queen, first book of a trilogy, Mercedes Lackey introduces the world of Valdemar.
I read all the three novels in a row, and in my opinion, they could have been squeezed between one pair of covers, omitting some flash backs the two sequels had.
The writing is more suitable for YA level, but some "grown up" themes probably forced these novels into the adult fantasy shelves.
The story is way too one dimensional Cinderella tale for my taste. At times it felt that the author had written a bunch of separate scenes and slapped them together forgetting the necessary glue in between to knit together a solid story. It was too predictable and naive to be truly enjoyable.