I first read Taliesin in the eighties (when it first came out), and I loved it. I went on to read and re-read the whole Pendragon cycle, and (even better I think), The Paradise War trilogy. For me, Lawhead took over where Rosemary Sutcliffe and Geoffrey Trease left off. He writes well, at times powerfully, and his retelling of the Arthurian cycle rings true for the most part.
There are niggles: I notice the ham-fisted smearing of Christianity onto an otherwise consistent tale far more now than I did twenty years ago. His use of Welsh is questionable, and (for me the worst of all!!) every feast sees mounds of potatoes being prepared... which is some feat a thousand years before Raleigh brought them back from America (or even two hundred years before Prince Madog).
Overall, though the story overcomes the historical errors, and sweeps you along. The interweaving of the two narrative strands heightens the contrasts between old, jaded Atlantis and the young, passionate Britain. It also sets up Charis, Elffin and Taliesin, as credible protagonists before they even come into contact with one another. As I said, I'm still re-reading these books twenty years after I first bought them.