A great deal of research and archaeological findings have taken place since this classic was first published. Nevertheless, I recommend this comprehensive volume for its wealth of description of Celtic iconography and other evidence. Scholars may justifiably differ with some of Ross' conclusions, and her work is not popular with those who believe that the Celts did not have a culture distinct from their Indo-European neighbors. However, she remains a careful scholar who shares her evidence and insights in a fashion that even newbies will find interesting and highly readable. To learn about more recent findings, also take a look at the works of Barry Cunliffe.
Definately not for the beginner in Celtic studies, while the book is archaic in some of its terminology and scholarism, it still offers a fairly good resource for those wshing to learn more about the Ancient Celts.