This trilogy, set in Celtic Ireland roughly at the time of the Crusades, deals a lot with history, myth, the Otherworld and even Christian mysticism. The story is an intricate knot of many threads, leaving the reader with few, if indeed any, cues on the final outcome. The characters span from down-to-earth Irish and Norman warriors, through monks, druids, seers, knights, and spirits to young and old goddesses themselves. A rich and and tasty broth!
However, while the tapestry is well woven, my joy reading it was marred by two factors:
Firstly, I found the style of telling a bit annoying. The story is told by an old woman, relating what she experienced in her youth. While a fair way to write the book, the old crone is a bit overly tedious now and then. She has a habit of not only berating herself for her youthly mistakes, but also of spoiling the story by revealing hints of what will come long before it should be told. While that's the way you do it if you really tell a story by the fire-side, I'd rather not see it in a book.
Secondly, the finale of the story is too twisted. While reading the book I gradually built an impression of what the story was "really" about and what the characters were "really" like (like who's evil and who's not). At the end of the story, however, some of these impressions were proven outright wrong - and the hints were never there to be seen. That makes me feel genuinely misled rather than tricked into misleading myself - the latter is fair game, the former is not.
Still, you may not share my views, and the books are worth reading!