I'm not really sure what I thought of this one. It's really a mystery with some paranormal elements than a straight up UF like the Otherworld series. That's OK with me and I found myself really intrigued by the setting of Cainesville (I have my theories about what's going on there) but I'm not sure I liked any of the characters.
Both Olivia and Gabriel struck me as extremely manipulative and seemed to treat other people mostly as tools. There's a lot of talk about sociopaths in this book, which seems natural given that Olivia is finding out about her birth parents who are convicted serial killers. I don't know if that kept in my mind more than usual but I just kept thinking that Olivia and Gabriel also show a lot of behavior that's slightly "off". I can't tell if they're just kind of closed off or if they really do have some anti-social tendencies, nothing truly violent, just the lack of thinking of others at all. It kind of plays into my theory of Cainesville (spoiler tag even though it's truly just my speculation)(show spoiler)
So, there's that. I also didn't love all the references to Olivia's economic situation and her desire to "make it on her own". Easy to live as a waitress when you have a trust fund coming due. And you meet successful people who seem to want to give you things. But that was more of a pet peeve.
The "Omens" in the title are really interesting and I did like the way the book built the supernatural stuff up as it went along. Olivia doesn't really know what's going on and is going on instinct and some vague memories when she realizes she sees omens that others may not. And I liked that we're learning it along with her. In some ways this definitely felt like a Book 1 (which is it) and there's a lot of set up and a lot of breadcrumbs to keep you intrigued in the town revealing its secrets.