This was pretty good. Certainly well-written. At times, I was totally picturing this as a movie playing in my head. x)
This is very plot-driven, focusing on three well-drawn enough characters, Indigo, Ariel, and Neko. Though I gravitated towards Ariel and Neko mostly, since it's so easy to sympathize and suffer with them, while Indigo was being a stubborn and (albeit rightfully) bitter bastard. There are some familiar aspects in the storyline, in regards to the whole Serenity vs. Chaos (basically Heaven vs. Hell), corrupted Church and the Covenant, warriors/Palets who have lost their purpose, and a rising sense of war (which doesn't happen in this book yet). But Wilder keeps it fresh enough with some new and interesting concepts, like the "artifact", what the hell Neko exactly is, and the Seraph.
There also is enough emotional angst for your heart's content in the epic, tortured romance between human Indigo and Ariel, his fallen angel and Guardian. I wouldn't mind seeing a prequel detailing the start of their 25 year relationship, when Ariel was first assigned to a much younger and still idealistic Indigo. Present Indigo is wracked with intense guilt over his part in Ariel's now mangled wings so he spends much of the book in constant emotional turmoil while forcing Ariel to stay away. His guilt is understandable but he treats Ariel rather horribly and I wanted to strangle him with my bare hands more than once.
But their angsty romance hit the guilty pleasure spot for me and the love scenes were hot and emotional enough, so romantic me was satisfied on that front. Although, (Don't look if you're seriously thinking of reading this!)
Then again, if it wasn't an HEA, I probably would be complaining too.
This book can stand on its own, there are enough hints for you to figure out how this Second War will play out. Ch. 36 is a good ending for Indigo and Ariel's story.
Except for that last damn chapter.
So 4.45 stars for now, I'll be sorely pissed and disappointed if she just added in that last chapter and is not planning to follow through..
UPDATE: So there WILL be a sequel! Not for awhile though. 3 books planned for the series.