I seem to remember having read
Hero with a Thousand Faces by Joseph Campbell around two years ago, but unfortunately all copies from the library are on loan now... can anyone remind me what Campbell's idea of the gods were? I'm pretty sure he did comparative religion--from Hindu traditions to Christian to Greco-Roman, even a bit of African. When I read that book, I was reminded of the structures of Tolkien's Valar, but unfortunately I can't remember how anymore.
Anyway one of the main points of that book (or maybe I'm confusing it with another book, called
Ishtar Rising) is "there's nothing new under the sun"; in Mesopotamian and Indo-European traditions, there is a theological family tree (if I may use that term), and that is why we see similarities like Astarte/Ishtar - Aphrodite/Venus - Freya. Usually goddesses of fertility are associated with crops, as with Freya's and Ishtar's case, but the Greeks have a different crop goddess, called Demeter, who we may associate with Yavanna. Now because of Roman Catholic tradition that devilized the goddess of love and sexuality, there emerged a new goddess-figure--the Virgin Mary and other virgin martyrs like Santa Ursula--and I think this is one of the most influential in Tolkien's myth-making. We don't see Aphrodites in Middle-Earth running after cute little mortals, or Freyas bedding Dwarves so she can have pretty jewels. But we can still see the older myths' influence in it, like Yavanna as fertility goddess and Varda as the Juno-figure, and the stuff
Gwathagor has mentioned.
I admire Tolkien for this, that he is able to put up a myth but not sound too stereotypical or archetypal.
Maybe because, in a matter of speaking, he got there first? Well, not really first, but comparatively earlier than other books that also has its own set of gods.