Richard Beams is the director of Opera con Brio, an opera-education program that is now in its 25th year. He is also assistant professor at Pine Manor College, a past recipient of NEH fellowships in both Opera and Literature and Verdi Studies, and a pre-opera lecturer for the Boston Lyric Opera.

Q. Many people know the overarching themes of the Ring cycle. Are there other, more obscure themes that are usually overlooked?
A. Themes are plentiful indeed; I'm not sure which are secondary or primary. Certainly the work is about man's conquest of the natural world for his own use (the spear was carved from a branch torn from the World Ash-Tree, as was the gold torn from the Rhine).  It is about man's dominion over men (benevolent oligarchy and capitalist tyranny are both condemned). And it is of course about man's understanding of himself (driving forces are soon discovered to lie hidden within oneself; [see] N. B. Robert Donington's brilliant Jungian analysis, Wagner's “Ring” and Its Symbols).
Andrew Porter, in his 1974 article “Wagner and ‘The Ring,’” sums it up well:  “It is not too much to claim that The Ring is at once a capital entertainment; a world history in allegory; and an analysis of man's psyche conducted with vivid, eloquent symbolism, both theatrical and musical.”
Finally, I think we should always remember, as our question suggests, that we are talking about mythology. The actual plot of the four operas is of much less significance than subtle ambiguities of meaning hidden in the events themselves and the appeal to the subconscious that myths have always held for us.

Q. There are some inconsistencies in the Ring cycle. For example, Wotan says he lost his eye while fighting for Fricka, but the Norns mention that he sacrificed it for the sake of wisdom. Which is true? And was Wagner aware of these inconsistencies?
A. There may seem to be inconsistencies in the Ring cycle, but Wagner really knew what he was doing and was certainly aware of these; in fact he probably created them purposefully. They make us look carefully at the text and listen carefully to the music. I refer your readers to Deryck Cook's brilliant analysis I Saw the World End: A Study of Wagner's Ring, where he deals with the logic behind many of these. In the example you raised, both [explanations] are true, if you dig into the mythology.
Wagner alters mythology drastically in order to give Wotan a quite different main motivation (that is, he is not just a battle god). The spear is not a mere invincible battle weapon made by dwarfs (mythology). Wagner has Wotan make it himself from a branch of the Tree of Life, as a direct consequence of his drink from the Well of Wisdom, granted in exchange for one of his eyes; Wotan dominates the world with it, not as a weapon of war but as an instrument of law (treaties, contracts, etc.) whereby he attempts to build up and control an ordered civilization of an authoritarian kind.
Wotan's attempts to evade his own laws will not be overlooked, and of course this is where Fricka comes in. Fricka attacks him in Rheingold for seeking to evade those laws in drawing up a fraudulent contract to increase his power.   
Indeed, Wotan says to her (in scene 4 of Das Rheingold):  “Recall the days when I wooed you, when I for Fricka paid the price of an eye.”  There is no basis for this in mythology, and certainly it seems to flagrantly contradict the First Norn's statement that it was for a drink from the Well of Wisdom that Wotan sacrificed his eye.
Yet, as Deryck Cook points out, there really is no contradiction if you assume Wotan is thinking of cause and effect: his drink from the well, enabling him to cut from the tree the spear of world-domination-through-law, inevitably brought him a wife like Fricka, enshrining the ideal of the spear. She becomes in the Ring a concrete symbol: the keeper of the ruler's conservative conscience—she too wanted Valhalla built (really to keep her husband at home)—but she is appalled at his disregard for law in striking the fraudulent contract with the giants.
Answers in Wagner are rarely simple!

Q. Has Wagner, in any of his writings, ever discussed the incidence of incest in the Ring cycle? And is it generally known that Brunnhilde is Siegfried's aunt, as Anna Russell pointed out in her parody of the Ring?
A. Yes, Wagner indeed in his writings discussed the incidence of incest in the Ring. In Opera and Drama (1850) he gives a vindication of Oedipus and Jocasta and then goes one with a lengthy attack on the idea that there can be anything harmful about incestuous love when it happens unwittingly between two people who meet one another as strangers. First he dismisses incest as genetically harmful:

Did Oedipus sin against human nature when he married his mother? Most certainly not. Otherwise nature, violated, would surely have revealed the fact by allowing no children to issue from his marriage. But nature, in fact, showed herself entirely willing. Jocasta and Oedipus, who had met as two strangers, loved each other, and were only disturbed in their love from the moment when it was made known to them from outside that they were mother and son. Oedipus and Jocasta did not know in what social relationship they stood to one another; they had acted unconsciously, according to the natural instinct of the purely human individual. And from their union sprang an enrichment of human society, in the shape of two strong sons and two noble daughters.

Wagner then goes on to put the argument, properly, in the social sphere:

In family life—the most natural, but the most confined basis of society—it had become established, quite of itself, that a completely different kind of attachment develops between parents and children, and between the siblings themselves, from that which makes itself known amid the sudden and violent excitation of sexual love. In the family, the natural bonds between the begetters and the begotten become the bonds of familiarity, and again, only from familiarity does a natural attachment develop between the siblings. But the first fascination of sexual love is awakened in the young by someone unfamiliar, someone confronting them newly from outer life; and this stimulus is so overwhelming that it draws them out of the family circle, where they have never encountered it, and impels them towards experience of the unfamiliar. Sexual love is the disruptive influence which breaks the restrictive barriers of family life, so as to enlarge it into the wider world of human society.

Like Oedipus and Jocasta, Siegmund and Sieglinde are entirely “unfamiliar” to each other when they meet, and have long since been in no danger of staying within “the restrictive barriers of family life,” since they are already members of the “wider world of human society.” Wagner, in inventing the love relationship between the long-separated Volsung twins, made it the absolutely central symbol of Act I of Die Walküre: it stands there as a great flowering of human love, in opposition to power (Hunding's power, Hunding as possessor of the unwilling Sieglinde) after the power-ridden, loveless world of Rheingold. Incestuous though it was, Wagner lets the lovers rejoice in it—and Wotan never gives way to Fricka on this matter.  (Of course he can't escape from her other point, that Siegmund is not a free hero but his own pawn.)
Answers in Wagner are rarely simple!

Q. Now that filmmaking has become so sophisticated, do you think there will ever be a movie of the Ring cycle in the style of The Lord of the Rings?
A. At last, a simple answer: I don't know.  However, I refer your readers to the excellent article by Alex Ross in the New Yorker (December 22 and 29, 2003) entitled “The Ring and the Rings: Wagner vs. Tolkien.” The article points out how The Lord of the Rings dwells in the shadow of Wagner's even more monumental “ring of the Nibelung.” The article also shows how the film “extends its grip through the medium of music, the work of the gifted film composer Howard Shore. . . . Shore manages the admirable feat of summoning up a Wagnerian atmosphere without copying the original.”
A movie of the Ring in the style of The Lord of the Rings?  Let's hope so; it would be a lot better than some of the onstage productions we get thrown at us these days!