It's been a while since I looked at her stuff directly (as in, almost a decade--geeze), but her early work is strong but dated. Her later work is more off the wall, and I want to say that book is the transitional one. It's not like her data is made up, but her conclusions are a bit off the wall in places. So she's right, but not nearly as right as she thinks she is.

There's a good quote in this New York Times article (worth reading):

But many other investigators of prehistoric Europe have not shared the enthusiasm. Bernard Wailes, a professor of anthropology at the University of Pennsylvania, says that most of Dr. Gimbutas's peers consider her ''immensely knowledgeable but not very good in critical analysis.''

''She amasses all the data and then leaps from it to conclusions without any intervening argument,'' Mr. Wailes said. ''Most of us tend to say, oh my God, here goes Marija again,'' he said.

Her work is really important because it rejected some ideas that came before her and a lot of her critiques have become common knowledge. So what she wiped away was important, but what she built up in its place, to put it politely, certainly isn't the mainstream thinking. Her work is more important today to the women's movement and feminist studies than it is to religious studies and archeology. Terms like that are usually used to describe dedicated amateurs, and I want to emphasize that she is no amateur. Everyone respects her erudition, but her conclusions are a bit off.

And she wasn't alone. She came up in a time (or really helped create a time, more exactly) where her conclusions about "Old Europe" were common knowledge. Her ideas, though, are quite dated, as are the people she was arguing against. The modern go to book on this period (and well the transition from it) is David Anthony's The Horse, the Wheel, and Language, which I sadly have only opened once or twice so I can't give you a more detailed view of it.