I really loved this series by Mercedes Lackey. I have always been a little ambivalent about her Valdemar stuff, since I've found some of it to be better than others, but this was the best I have ever read and not just because Lackey is handling a homosexual relationship in sf/f with tact and grace and not simply as an excuse to make the bad guy evil by having him sexually abuse boys.
Her characters are incredibly real, especially in this book. They tend to fall into the fantasy character trap of being slight caricatures of themselves and doing either hte perfect thing or the phenomenally stupid thing to prove they're not perfect. In either case, it's a genre-wide fault and one that I will willingly forgive Lackey, since the rest of the story was so gripping. Despite its flaws, I was more than willing to overlook them and enjoyed the books tremendously. I found it nearly impossible to pause between them and, when I put them down, it felt like I was parting from good friends.
If you're a fan of the genre and think that it's time that slash took its place in the mainstream, you have got to read this series.