It's a look at what Irish myth and deities might mean to the Irish today -- and to the human race more widely.
Moriarty in no way self-identified as part of the "Pagan" movement. He would have said the he was a Catholic. However, his take on spirituality is so unusual, informed by world myth and folklore, and very heavily by nature, that you wouldn't pick that up at all from reading this book. He is no John O'Donohue although he is a kind of poet philosopher that's about the end of the similarity.
Some of this book is hard going, when the multicultural references come a bit thick and fast, most of it is beautiful and some of it is an easy ride, some parts are as edgy as an acid trip.
All this is to say "I can't really describe it. I tried that in a very long blog post, and it was still difficult."
If you want a taste of what this guy is about - try this video http://youtu.be/m6kfo4FahM0
It's how I got hooked. There are a number of other good items with Moriarty on YouTube, too.