This is the first book of a trilogy; and like Tolkien's Lord of the Rings books (which he originally didn't want to separate into three volumes --that was the publisher's idea), the Song of Albion books basically form a unit that should be read and considered together. An evangelical, Lawhead displays the influence of C. S. Lewis in places in his writing; the Christian symbolism in the last volume, The Endless Knot, is particularly clear. But his fantasy vision is his own, heavily influenced as well by Celtic mythology (American born, he moved to England to have better facilities for studying Celtic history and culture), and his fantasy world is supposedly the Celtic Otherworld, with a recreated Bronze Age Celtic culture whose elements of primitive monotheism he stresses (more so than they were in actual pagan Celtic society). He makes very creative and original use of different features of Celtic lore, such as the Silver Hand (which provides the title of the second volume), the endless kettle, Beltane fires, etc.
Lawhead is a capable stylist, skilled at creating absorbing plots, characters, and atmosphere; he does that here, and (as expected from an evangelical writer) there are no problems of bad language or sexual content in the trilogy. It is, however, very violent (a trait more marked in the last two books), with a good deal of grisly killing, massacres, blinding and beheading, often with the innocent, and characters the reader likes and cares about, on the receiving end of it. This is a reflection of a clear-eyed awareness of the capacities and results of human evil, squarely faced; but it's definitely not for the squeamish.