The question of paganism in europe doesn't present itself immediately as a matter of scandal, though the relative absence of histories on the subject does at least hint at the controversy of the topic. Usually relegated to Folkloric studies (with their classifications and archetypes) the issue of paganism is miserably under-treated.
Contention exists over the very definition of pagan--the general "western-academic" consensus is that it is a useless or over-used word, stolen by new-age neopagans to mean something somehow universal. History usually attempts to draw straight lines through time, successions of tendencies and thinkers one after the other until the present (or until the death of the idea), and is more than happy to this sort of thing as long as funding for "history of science" grants continue. Everything that can fit into the grand-narrative is important (or, conversely, nothing that has already been used in the grand-narratives matters), leaving the question of pagan/indigenous beliefs of europe to the celtic-tapestry lot (of which, i'm told, i belong).
So, what then to make of the libraries and archives full of catholic denunciations of "pagan" practices remaining all the way into the 19th century? Offerings at well, shouting at the moon, refusing to eat certain animals or drinking certain things on certain days. Injunctions against paying any attention to the phase of the moon at all are rife. The Catholic (and its reformist-children) church has long tried to uproot these practises, and as facile as it might be to attribute such tirades to religious hysteria, the fact people that some people still throw spilled salt over their shoulder or that most of old bretons in northwest france still tie ribbons over "fairie wells" (i've seen it personally) suggests that the pagan-tendency was never fully uprooted.
So, come we now to Jones and Pennick. Their book is an inadequate (but welcome) addition to the shelf that so far only contains books like The Golden Bough. Slim (288 pages), well-researched, but unsatisfying. I don't mean to be hard on them, seeing as how they couldn't seem to secure any sort of funding whatsoever for their subject matter (and received rather vicious reviews by folklorists for disturbing their comfortable calculus). But it's too small, a tiny drop in an drained pool. Still, since it's something at all, and more than interesting to read, i highly suggest it. Work on the lithuanian pagan kingdom is appreciated (not original, but most wouldn't know where else to turn), but the sense that they're screaming into the wind is difficult to shake. They know they're not wrong, they're not being foolish, and yet they seem to apologise almost--take us seriously, they almost say, even though the reader probably already is. I did, i still do. But having read other accounts alluding to the same periods, i can't help but think they could use a little more confidence.
One thing they do well, however, is begin to place european paganism within the context of other paganisms. One of the biggest objections to anyone beginning to address the issue is the right-wing tendency of some european and anglo paganisms: every white-boy software coder was pretty certain he was scottish after Braveheart, and not a few of them used this new-found heritage to argue against other indigenous-rights movements (scots were an oppressed people, too, and so why are all the american First Nations complaining?). There's a way out of this, and it seems humorously simple, though one needs to look elsewhere (I suggest India: Chakrabarty and Leela Ghandi). J&P begin some of the work to link paganisms outside of racial/tribal groups (race didn't exist as a notion till the 19th century--is no one reading Hannah Arendt anymore?), and a lot more could be done, but again we come back to the question: why should J&P have to apologise for a bunch of white idiots at Microsoft calling themselves "goths in the traditional germanic sense"?