Everfound was more enjoyable than the previous books in the Skinjacker trilogy, both of which I found quite slow for their first halves. It took me those two whole books to really become invested in the characters and their fates.
In my review of Everwild I discussed briefly what makes Mary Hightower a really great villain, and she continues to be so until the (very) bitter end. There's nothing more dangerous than a deluded person on a self-appointed mission, especially if they are able to persuade others of their righteousness by appearing like a saint. I don't know a whole lot about the myth of the Anti-Christ, but I think an interesting comparison could be made here.
Shusterman explores a lot of themes in this trilogy, including friendship, morality and redemption. Many of the characters find themselves on an archetypal heroes journey, but each walk a unique path, discover a different purpose, and end up at a different destination. Not everyone in this series gets justice.
I was a bit weirded out by the mass violence perpetrated on the living world by the dead. It seemed surreal at times, and I had to keep asking myself if it was appropriate for YA readers. I mean, you can legitimately compare Mary to Hilter, but none of the characters in the story seemed to really grasp the full horror of what she was doing, and some of them even afforded her respect at the end. Is it the knowledge of life after death that makes her mass murders more acceptable? Or is it because they knew her personally and couldn't see her as a monster? Or perhaps being removed from the land of the living themselves, Afterlights were too disconnected to value life the way the living do. Maybe, though, it was just a fail on the author's part.
In any case, as a whole, the Skinjacker trilogy is a unique story that explores some interesting themes in a palatable way. Everlost is a fun realm to read about, and Shusterman has created a host of compelling characters. This series is written a little "young" compared to most YA books I've read, so I'd say it straddles both the YA and Children's genres.
See my review of Everlost (Skinjacker #1) and Everwild (Skinjacker #2)