Much has been remarked about Tolkien's Catholicism and how this plays out in Lord of the Rings. Much less known, or more precisely much less tolerated are his earlier efforts to create the myths of Middle Earth, later packed by his son into The Silmarillion.
These stories are for the most part told at a high level of summary, which sucks a lot of the potential drama out of them, though to me at least they still hold some appeal. What interests me at the moment is their status and value qua intentionally created myths.
This is an area that's fairly new to me; I'm familiar with Joseph Campbell and get the idea that certain hero-types and other tropes reoccur through disparate mythologies, but the value of myths and their relation to religion and to modern entertainment is not yet clear to me.
Karen Armstrong argues that "mythos" is the important aspect of mythology, as opposed to "logos," or actual doctrine that you're supposed to believe. Religion deals with what is by definition beyond rational expression, and since we can't accurately say anything literal about it, we deal with it through stories. Hence, the best way to read, say, the Bible is allegorically. But as Dawkins points out, the lessons of some of the Biblical stories taken as allegories seem pretty horrible: Abraham being lauded for (almost) sacrificing his son is supposed to teach us what? That blind obedience is good? No, thanks; I'll pass.
So what do we see in Tolkien's world? Well, much of the same. Elves, the first-created children of Ilúvatar (the big god who's deist at best; his assistant gods whom he created are the ones actively interfering with things a la the Olympians) are summoned for their protection to come to the home-continent of the Valar (the assistant gods), and most do so, but eventually their pride--assisted by the lies of the bad god (Morgoth, i.e. Sauron's boss) which their pride opened them to--caused them to leave, back out into Middle Earth where crappy things happened to them for thousands of years until they eventually all slunk back to the Blessed Realm (during the Lord of the Rings). So, the moral is "stop being such ungrateful bastards who feel you have to think for yourselves and take control of your own lives!"
Maybe the most interesting element to me in Tolkien's setup is the place of humans: We're Ilúvatar's second attempt to create children (oddly, one of the lesser gods tries to make some of his own, i.e. the dwarves, and Ilúvatar gives him a conditional smack-down and says that his creations have to go to sleep for many years until after Ilúvatar's own creations are all active, and only then can they wake up and join the party), and the innovation is that we humans have been given "the gift of death." So whereas the elves (and Ents and some other things) have to just keep on going and going until they're all weary of existing for thousands and thousands of years, though they can maybe drop off to sleep or hang out in the halls of Mandos (like Valhalla), we get to die off, which gives us an existential challenge of getting out there and making something of ourselves before that happens. Yay!
And sure enough, in a later part of the story (the Akallabêth), the men that the gods love best, who get to live a few hundred years, be extra tall, and hang on their own island close to the Blessed Realm... they too get all prideful (and filled with lies, this time from Sauron in a less ugly guise than a big armored goon or a vaginal-looking eye on a tower), and resent the fact that the gods didn't give them immortality, so they violate the gods' commandment not to sail to the Blessed Realm, at which point their island gets sunk and the portion of Middle Earth where most of the story takes place also gets all flooded (so the Entwives, for you LOTR fans, are most likely all seaweed at this point. Sorry!), showing that once again, you bastards better all remember your places and not get too high and mighty, or the gods will smack you down.
In conclusion: I think these manufactured myths are an improvement over the myths of the Old Testament, with a lot less filler and commandments about stoning, and I find his blending of monotheism and polytheism opens up a lot of story options, with overt conflicts between gods yet a secret plan by the big god behind even those. Still, with Tolkien being so thoroughly Catholic, his myths retain a lot of the downers of his religion, i.e. man is a punk that needs to be kept in his place.
This leaves open the question of whether Tolkien has done us a great favor by providing something to engage our need for mythology that is less damaging than traditional religion, and beyond that, whether a good chunk of our popular entertainment is doing the same thing. In the Middle Ages, people's need for drama may not have had many more outlets than Biblical stories, but now we've got Spider-Man and teenage vampires and Dexter and all the rest of it. Does that fill the spiritual vacuum?