I really don't know how to categorize this book.
I mean, for a while, I thought it was a serious fantasy book. Then things got way crazy and I thought it was a comedy. Exactly at that point, craziness went out and things were not funny anymore.
Maybe the guy just read too much Irish tales and decided to write about it, since there are very few books in which the story happens in Ireland.
In the end, sure, it's a story around some Irish tales, based on Irish history and, basically, that. It's crazy, it's hard to follow and jumps around too much.