There's a comparative lack of scholarly works covering pre-Christian religion in Europe from a neo-pagan perspective; this one is a good start, despite some failings.
The authors set out to cover the native traditions of Europe over time, specifically the non-Christian ones. In 9 chapters, they cover 'The Greeks and the Eastern Mediterranean,' 'Rome and the Western Mediterranean,' 'The Roman Empire,' 'The Celtic World,' 'The Later Celts,' 'The Germanic Peoples,' 'Late Germanic Religion,' 'The Baltic Lands,' and 'Russia and the Balkans.' Primarily relying on the most stolid of historical and archaelogical evidence, they give an overview of the religious practices and change over time of the pagan societies they cover.
Each section forms a useful little introductory text. Deities, religious practices, religious elements of the society, and shrines are all touched on, with reference to both pertinent details and to change over time. Each section gives examples of survivals of pagan customs into later times (19th and sometime 20th centuries). Especially strong sections describe Etruscan religion and the development of Roman religion; treatment of the mystery cults in later Rome; specific temple/shrine sites in German and Celtic lands; and material on history in general.
Reading through the book, one discovers a decline in the quality and comprehensiveness of the material from the beginning to the end: the chapters on the Minoans, Greeks, Etruscans and Romans are quite good, while Celtophiles and Norse believers may have cause to complain that their areas are treated shabbily, and Eastern Europe results in a terrible muddle. Apparently reflecting the British historiographical bias, the Celtic section almost ignores Ireland, Scotland and Wales, while the Germanic tribes have more airplay than their Scandanavian brethren... though this may also reflect the Roman historical sources being used. The authors, in treating the Baltic areas separately, tend to lump the West Slavs (i.e. Poles) in with the Baltic Lithuanians and Estonians, and to completely fail to identify Hungary and the Magyars with their linguistic relatives the Finno-Ugrians. Mixing Russia with the Balkan states, some of which were South Slavic and some of which were not, is perhaps an error too. There is definitely a sense that in describing the Lithuanian paganism, the authors relied too heavily on accounts from modern Lithuanian neopagans, and in treating the Slavs, relied heavily on ethnographic analysis of folklore. However, the material contained herein is an excellent starting point, which should send the reader off to investigate further resources cited in the text. The reasonably acute reader should be able to figure out which references are the most reliable simply by checking the footnotes.
Notably for a book with a neopagan viewpoint, this volume is remarkably objective in its treatment, managing to get through most of its 220 pages without antagonistic references to Christianity, and to give a remarkably clear account of the transitions from pagan religions to Christianity not only in the Roman empire but in other cultures. Further, in the conclusion, the authors point out that the target of the Reformation witchhunts was not directly paganism, but 'magic as a diabolical pact', though it is possible that some of those accused may actually have participated in a magical religion of some sort. The conclusion also gives a good treatment of the resurgence of pagan material in the Renaissance, as well as the re-creation of Druidic and German practices as part of the Romantic paganism of the nineteen century. Despite a somewhat modernistic definition of paganism which includes "they recognize the female divine principle, called the Goddess" (a statement which I suspect Roman, Celtic and Germanic practioners alike of the pre-Christian centuries would dispute), the authors stick remarkably clearly to native pre-Christian religions and their possible survivals in Europe.
The book is immeasurably improved in importance by a selection of maps, diagrams, engravings and sketches, as well as a hefty bibliography. The index is quite good for a book of this type, though other reviewers point out (and I agree) that the footnoting and explanatory notes could have been more meaty.
As a first step into examining historical paganism from a scholarly viewpoint, and a useful background book to give neopagans an overview, this is an excellent work despite its many faults. Critical reading and liberal use of the bibliography will add value to the reader's experience. As Choice magazine pointed out in their review, serious students and scholars will be better served by reference to the many excellent works on specific cultures and religions; however, for those just beginning to investigate materials more factual and less interpretative than the average pagan manual and/or feminist religious studies, this is a good introduction.