Overall this was a pretty good start to a series. I liked the general concept of the four horsemen and their curses. That was something new and refreshing. The mythology and worldbuilding was great as well. Ione has created a very expansive world filled with a myriad of different creatures and species. The sex scenes were pretty hot and I was rooting for the couple by the end.
That was all the good stuff.
However, because this is a spin-off series there was a lot of time devoted to revisiting characters from the main Demonica series, and as I have only read one of those, and even that was some years ago, all of those sections were totally lost on me. That's when I found my attention wandering. Several times during this book my interest peaked and waned and peaked again. We'd suddenly swap to some characters (of which loads and loads were mentioned) who were recently mated and having a baby or just had some babies. And I'm sure if I had a clue who these people were it would be lovely to catch up with them. As it was, I was kind of bored. It's probably my own fault for reading a spinoff before the main series but I do also believe that Ione was a little overindulgent in her "name dropping" of Demonica cast members. You have to assume not everyone will know who these people are.
Also, because this is a well established world with a full series worth of worldbuilding under it's belt, a lot of that same info dumping had to be shoved into this one book and it was a lot to absorb.
So my advice would be that this is a good series, and even though you can follow the plot easy enough without reading Demonica first, in terms of enjoyment, I think mine would have been upped exponentially had I read them the correct way around.
I'm still going to carry on with the next book and hope that a lot of these issues will be gone or at least lessened.