If you are interested in this field Cicero's summary is a bit hard to
read but remarkable, possibly even breathtaking when you consider the
date. He raises most of the points raised on this thread and much
more.
Cicero, M.T. (60BC) The Nature of the Gods (Oxford Worlds Classics) by
Authors: Marcus Tullius Cicero, PG Walsh Released: June, 1998
Full text at:
http://trisagionseraph.tripod.com/Texts/Cicero.html
Best Wishes
Alex Green