There's a debate about video games that resurfaces every once in a while: whether games are art. To me, the answer is obviously yes. I'll say that my definition of art does not make any judgment on quality. Art can be cheap, it can be mercenary, it can be wrongheaded, but still art. While not all games have a narrative behind them (there's no "lore" to Soccer, Checkers, or Tetris,) a lot of games use the medium as a venue for storytelling, much as film, theatre (which you can expand to dance and opera,) poetry and pose often are used.
I'm not really interested in arguing for the art-ness of games here. Dark Souls does incorporate much of its symbolism and ideas into the gameplay features - fire and cycles of death and life are at the absolute core of how the game works.
For now, though, I'm going to attempt to piece together the lore of the game. There are many people who have done so - check out YouTube - but the game's story is so open to interpretation that I don't feel that I'm just rehashing things other people have said.
There are two direct sequels to Dark Souls, but I'm mostly familiar with the first game (though I'm following the news about Dark Souls III, which has been released in Japan and will come out in the US sometime soon.)
As the game begins, we're given essentially the origin story of the Dark Souls universe. To begin with, the world was a cold grey place where there were simply grey trees and the "everlasting dragons." Nothing lives and nothing dies during this period, and it seems to suggest that going back in time, it was simply always that way.
Deep below the earth, though, there were four beings who discovered "Lord Souls."
Right off the bat, there is a huge question here - what is a soul in this game? Later, the even bigger mystery of what exactly humanity is will also be raised.
These beings took on the Lord Souls and became Lords - gods, essentially. There was Lord Gwyn, Nito, first of the dead, the Witch of Izalith, and the Furtive Pygmy, the "oft-forgotten" fourth lord. These deities struck against the dragons on the surface, combining their powers to blast the scales off the dragons, plague them to death, and burn down the trees, beginning the age of fire.
The age of fire seems to have been, well, a whole age of normal human activity, with different cultures developing. But over time, the First Flame - representing the life of the world (maybe) began to die out. First, Izalith tried to create a new flame, but somehow this became corrupted, and she accidentally birthed demons into the world. Eventually, Gwyn sacrificed himself to keep the flame burning, allowing his own soul to be consumed. But in the end, this only prolonged the inevitable. As the game begins, the flame appears to be dying down once again.
Humanity has a growing affliction, which is the Darksign - those carrying it become undead, and cannot die (at least not permanently.) You begin as one of these unfortunate undead who has been locked away in the "Undead Asylum" because the rest of humanity just doesn't know what to do with you. Worse still, the undead gradually go "Hollow," becoming the mindless zombies we usually think of as undead.
So here's where things get interesting. Good and evil is not really the dichotomy that Dark Souls concerns itself with. By creating the First Flame, the Lords created disparity, and disparity leads to entropy.
A scientific definition of entropy is the amount of disorder a system has. Essentially, over time, the number of possible states for a system grows larger and larger. In fact, there are some scientific theories that entropy is not really defined by time, but rather the other way around - that we perceive time as going in one direction because of the flow of entropy. In a way this makes sense - there's only one past that exists, but there are many possible futures (you might chalk that up to simple ignorance of the future, but given how quantum mechanics suggest that the universe is not, on a fundamental level, deterministic, it actually seems to be literally true.)
The era of the everlasting dragons was one in which nothing happened. You never had to worry about anything ending (or at least, it was a real shock when the Lords emerged) because everything was just going to keep being exactly as it was.
But that doesn't seem very good, does it? After all, perfect stasis is pretty much just like death. If you had a person who was cryogenically frozen (if that technology existed) and you never thawed that person out, would they basically just be dead?
The Lords' emergence means change, and change means life. But that change is ultimately entropic. The energy output of the First Flame cannot be channeled back into fueling itself. Lord Gwyn's solution prolongs the Age of Fire, but the major message of the game is that it cannot be prolonged forever. Yeah, this isn't exactly a happy story.
What's interesting, though, is the way that the Lords embody disparity.
Nito, First of the Dead, represents - duh - death. There's more to say about this, but he's clearly representative of human death - he basically looks like a bunch of human skeletons bound together with a grim-reaper cloak.
On the other side is the Witch of Izalith, who could be argued as the representative of life. She brings creatures to life, but it goes wrong and they wind up being demons. She's transformed from humanoid into a giant weird tree-thing called the Bed of Chaos (no, I haven't gotten to her yet,) and while she's clearly unleashed harm upon the world, plants are most commonly used as symbols of life.
Gwyn represent light - he's the clear Zeus/Odin-style patriarchal deity, and his realm of Anor Londo is cathedral-like and filled with light (it's also the one place in the game that looks clean - which is a bit of a shock after spending so much time in crumbling ruins.)
In contrast, however, the Furtive Pygmy is clearly associated with darkness. The game suggests that "humanity" is actually a fragment of the Pygmy's soul, and it is passed down through all humans. One needs humanity to "reverse hollowing," which allows you to look like a normal human being instead of a desiccated corpse. Why is the Dark Soul different from the other three Lord Souls? Why did the Pygmy spread it to his offspring? I don't know.
The irony of all this, though, is that as the Fire burns out, the world might actually just return to a state similar to how it was before the Lords arose.
The origin of the Darksign is also a big mystery. We don't know what the Pygmy has been up to - there seems to be some suggestion that he might be Manus, Father of the Abyss, but I can't comment on that. Given his association with darkness, one could suspect his involvement.
But in a way, the Fires burning out kind of fits with the curse of Undeath. Being undead is a reversion of the disparity between life and death. You're not really alive, but you're not really dead. It's reflected in game mechanics - just as you just wind up back at a bonfire if you're killed, so too are most of the enemies in the game. No one can really die, but instead people go "Hollow," and so they can't be said to really be living either. The Fires going out would extinguish both life and death, and so if the world is reverting to the Everalsting Dragon era, it makes sense that humans would also be taking on an everlasting form - but one that has no disparity to fuel true living.
Probably the most confusing thing thrown into the mix here is the presence of Kaathe and Frampt, the absolutely ridiculous-looking... "Serpents?" These big-toothed guys with floppy mustache-tendrils each suggest different things. The goal of the game is to get to the Kiln of the First Flame and essentially put Lord Gwyn out of his misery, as he's gone hollow. One (I want to say Frampt) tells you to then "Link the Fire," giving your own soul over to it to fuel it for another age. The idea would be that while the Fire might have to go out eventually, as long as there are those who are noble enough to sacrifice themselves, they can keep it burning. The other, however (Kaathe, I think) tells you to simply kill Gwyn and then walk away, bringing about an age of darkness - the Age of Man.
And that's wildly open to interpretation. Humans seem to be connected to the Dark Soul - it seems that "Humanity" as seen in-game are fragments of that Dark Soul. So if humans are dark, then an age of darkness might mean an age in which humans become the dominant force in the world, which could be good or bad.
But are we to understand that the First Flame is simply that of Gwyn - the light, complete with patriarchal deity who is in charge of the world - or is the Flame the very disparity that allows both light and dark to coexist?
There's a ring called the Serpent Ring that describes Serpents as imperfect dragons. Could it be that they are manipulating the player into undoing the works of the Lords?
But Frampt and Kaathe both tell you to do basically opposite things.
They're both pushing you to kill Lord Gwyn - and the other Lords, for that matter (the Pygmy isn't in the game, at least not before the DLC, assuming everyone's right about Manus.) Could beating the game actually be the wrong thing to do?
Setting aside that tin-foil hat interpretation (I say tin-foil hat, but I imagine it's one of the many valid interpretations of the game others have had,) there's also a kind of odd irony when you think about the idea of linking the fire. The flame created disparity and change, but the act of linking the fire - preserving it - actually means preserving things the way that they were.
The Age of Darkness ending obviously sounds like the "bad" one, especially given that it plays into ideas of our hero doing something selfish - it's suggested that he or she will become some sort of god-emperor over the coming age, assuming the serpents aren't just lying to him/her. But perhaps it's actually better. The First Flame might have been the catalyst for the universe having... stuff happen in it, but perhaps it's inefficient in consuming the fuel of reality. Maybe there's a whole other way for the Dark Souls universe to be organized that allows it to be totally different things, and perhaps that's what the Age of Darkness entails.
But honestly, who the hell knows?