I've been listening to The Silmarillion during my commute lately. Being almost more an outline than a narrative, it's an odd experience listening to it, but I haven't read it in 12 years, so it's nice to get back to it.
On a side note, finishing the story of Baren and Luthien and having half in my mind all the recent Star Wars fan discussion of whether Rey is so competent that she doesn't need the male characters to be in the story, several things struck me:
1) The story of Beren and Luthien is about a couple. It's not primarily the story of one of the two, in which the hero wins a consort at the end. Nor is it a story in which two individuals figure out during the course of the narrative whether they can be a couple and unite at the end. While Beren has adventures before he reaches Doriath and meets Luthien, those adventures make up fairly little of the story. Also, while the love of Beren and Luthien is central to the story, it's not central as a source of conflict. There are not points where one doubts the love of the other. The conflict is all externally driven. (Perhaps this isn't surprising given the Tolkien wrote the tale both inspired by his marriage and as a sort of ideal for it. On their shared grave, JRR and Edith are identified by their own names, but also as Beren and Luthien. Tolkien wrote the first version of the story while he and Edith were apart because he was serving in WW1.)
2) The biggest deeds in the story (the rescue of Beren from the pits of Sauron, stealing into Angband to take the Silmaril from Morgoth's crown, etc.) are done by the pair of them together, and could not have been completed by either one alone.
3) Luthien is a character who shows incredible strength personal strength, both facing extreme adversities and also engaging in direct struggle against Sauron and later Morgoth (Sauron's master and essentially the Satan of Tolkien's universe, but one with a kingdom of terror on Middle Earth far mightier than Sauron's Mordor in Lord of the Rings.) However, she does not do this as the sort of "badass female character" which is so prevalent in modern popular fiction. Indeed, there's not a significant point at which she takes up any kind of weapon. This is partly in keeping with the fact that the Silmarillion is told in a mythic manner in which wielding swords and engaging in physical combat is often a lesser form of striving (indeed, one of the mistakes of the Noldor is in imagining that they can use physical war to conquer Morgoth without the help of the Valar.) At the gates of Sauron's fortress, Sauron attacks Luthien after taking on the form of a wolf. He's fought and pinned by Huan, the hound from the deathless realm across the sea, but it's Luthien who then by force of will compels Sauron to give over command of his fortress to her, and then casts him out of his body, leaving him nothing but a spirit. Similarly, when Beren and Luthien go to Angband to wrest the Silmaril from Morgoth, it's Luthien who puts the wolf Carcharoth who is guarding the door to sleep, and later even Morgoth himself. Yet in no way is Beren a background tag-along character, given that he both defeats Celegorm and Curufin (two of the most powerful elven lords) when they try to kidnap Luthien, and also hunts and kills Carcharoth himself, not to mention that it is Beren (a man) who succeeds where all the mightiest of the elves have failed in taking back one of the stolen Silmarils. Beren and Luthien are both "strong characters" but their strengths are different and complementary.
This last point also ties in to the sort of world which Tolkien has created, which is a world in which not every problem can be solved at the edge of a sword. Beren is brave, a skilled warrior, an honest man and keeper of his oaths, a tracker in the wild, a friend to birds and beasts, and is willing to suffer great pain. Luthien inspires deep loyalty (the loyalty of Huan is several times key to the success of their quest), she is perhaps even more brave (when they come face to face with Morgoth it is Luthien who faces him while Beren is hiding in disguise), she has a strong will and strives with fallen angelic creatures such as Sauron and Morgoth, her songs can exert power over others, she senses at a distance what is happening to those she loves, and she heals. There are points where Luthien would have been killed or kidnapped but for the physical protection of Beren, and others where Beren would have died of wounds, been left in captivity, or been daunted by wills beyond his strength but for Luthien. Both at times seem much more vulnerable than the other, and both at times seem much stronger. However, they're never in competition with one another. Because again, the fairly unique thing about this story is that it's a mythic adventure story undertaken by a couple as a unity.