I've really enjoy reading the whole Warder series. It's a fun verse, and I like how well the warders mix their ordinary lives with their warders lives. Book four was definitely my favorite, and I think one and four were the strongest.
Let's get the nitpicky stuff out of the way: Sometimes, I think there was too much telling and not showing. But it was minor, and not a huge detractor, and I know there are peeps who like to have things more explicitly spelled out. The other was that we did not need a recap of warders, hearths, etc every single book. That would be fine if the books were meant to stand alone, but they really don't make sense if you don't read them 1-2-3-4-5 so having all of that re-explained every time was a bunch of text I just wound up skipping.
All that being said, the books were a hell of a lot of fun. The first one is a great introduction, being from the POV of the love interest, rather than the warder (all the others are from the warders' povs). If you go into the book blind, you might think it's just an ordinary contemporary novel until suddenly it's not, and that's a great execution ^__^ One of the best intro books I've ever read.
My other favorite part is that the books aren't all about new couples. 1 & 2 are, but they're very different in nature, and the rest of the series is about established couples, or, in the case of Sinnerman, about a relationship that fails. That's one of the reasons the fourth is my favorite--the warder catches his hearth cheating, and to see that it's not always sparkles and light is cool to see. Plus I really like the new love interest, I was in love with him from the first moment he appeared :3
I loved all the characters and side characters, the dynamics, how the whole thing functioned. It's all very well put together, down to the last detail. This really was a great series. I was sad it was not in paperback when I went to Yaoi-Con, because I would have killed to have them in print for her to sign. It's the kind of world that makes me want to do fanfiction.
If she ever decides to play with a new set of Warders, I am so there ^__^