Ending confusion

Is there truly a good or bad ending? I mean, link the fire, you could say, is just 'fixing the dam', but eventually it will start to burst again, and someone else has got to fix it, and thus history repeats, and more undead get hollowed in the process. the dark lord ending proves that the dark lord has returned, and the age of mankind is ushered in, but, the dark lord ending also proves to me that the abyss will spread, and it has show that it can devour entire towns like Oolacile. so you have brought about the end of lordran and possibly the world. Truly, this game is just one tragic story, and no matter how hard you try, you can't save everything in Dark Souls.

Just like real life.....

Save everything? By the end of the game, you've killed almost every living thing in Lordran.

Honestly, I believe that Linking the Fire is the good ending. Going based solely off facts and little to no interpretation: Dark Lord is bad. The dark wraiths gladly suck out the souls of their own species for their own twisted ends. The Abyss is OBVIOUSLY evil and corrupting, as we see in Oolacile. We also know that the undead curse is linked to the flame dying, as the intro implies that the undead are a relatively new phenomenon, hinting that it happened quite a while after Gwyn linked the flame. After all, pyromancy has really only been (actively) around for ~200 years (not STRICTLY proof, but evidence).

In contrast, while it's likely that the Flame will start to die again, it's also possible that the return of the Lord Souls will stabilize it. However, even ignoring interpretation, there is little to suggest that the world would be better off without the flame, despite what Kaathe says.

So while we can't truly KNOW what would happen in either scenario, I find it far more likely that the Link the Fire ending is the morally righteous ending.

Also, most of what we kill is undead, not living Lance

To Link the Fire makes sense though, another undead hollow will need to do the same thing. That's not a bad thing for us, it just starts NG+ in a more logical way.

Oh and by the way, just remember that it can be even more depressing than you think. Just for the record the "chosen undead" is nothing more than a pawn being used by either Frampt or Kaathe. So really nothing you do will really mean anything because the character was being used this whole time by one of the Primordial Serpents.

...

Or you can just skip the dialogue and pretend you have you're making your own choices.

I think the endings are a lose-lose situation. In one hand, the Abyss begins a much faster expansion, presumably enveloping the entire world. After looking at Oolacile and the ruins of New Londo, I think that is a really painful existence. On the other hand, based on NPC descriptions and hints at what the world outside is like, especially in religiously devout areas, I question how much better a world ruled by the gods are, if any. The religious community seems to share a punitive, self-righteous dogma similar to the Spanish Inquisition; (listen to the Crestfallen Warrior's theory on Anastacia, the comments from the Undead Merchants on how they were treated outside of Lordran, all the lies and secrecy on the gods' part) the world outside of Lordran is essentially all of the very worst aspects of the Midieval Ages and Renaissance, and the dogma preached by the gods is apparently a large part of that.
Something I do find intriguing is that Fire essentially represents the Gods, whereas the Abyss and Dark represent Man/Humanity. It's possible that the Abyss was not spreading until the people of Oolacile awoke Manus and got him really mad. Even Hawkeye Gough said '... toothy serpent or no, they awoke that beast themselves." Miyazaki, the game's director, also said that he aimed to say in the game that humans are essentially good. If humanity is good, then it seems pretty paradoxial to me to have the Dark, the very essence of humanity, be innately evil and that to be good must enslave themselves to a collection of gods that have lead them into such a society. I think both endings are loss for the Chosen Undead unless he or she is evil, actually wants everyone undead, or is blindly devoted to the gods.

I interpreted both endings as the "wrong" choice. Basically, at the end, your character is only capable of two choices. As Arcanatia and others have pointed out, there's seemingly major issues with either choice.

In the end, you wake up back in your cell, with your memory intact and most of the loot you found still where you left it. You're not a new Chosen Undead, you're the same one, exactly as you were after you beat Gwyn.

I think the two endings are interesting ways to choose a side but both me represent the futility and powerlessness of an individual on a cosmic scale, which seems to be ever present in the game. Gwyn and his company have a vested interest in their hierarchy and the flame, yet can't maintain it. Even collaboratively, the Gods are powerless in the end.

The game play hints that the world existed before the flame. This world without "fire" didn't last either. The darkness is no better at thwarting the whims of the cosmos than the fire.

We, as individuals can have a major impact on what we consider the world. But in the end there's no difference. Everything balances itself out eventually.

Going back to my statement that they're both the "wrong choice" I mean that your character is only presented with two options, linked to one tiny aspect of the universe....a flame. The decision you are left with isn't actually relevant to existence.

I believe that the Dark Lord ending is the "Good" ending. The Fire represents the Gods and the era of light is essentially the "Gods Era" whereas the Dark represents humanity and the human condition. Now, in almost all forms of media there are two things that we are forced to swallow.

Light (Fire) = Good

Darkness = Bad

In Dark Souls, I don't think this is true. I like to think of it in the Final Fantasy III (may a pox be stricken upon my house should I ever compare DkS to FF again) in that Dark and Light are neither inherently good or evil, but instead what they are used for designates whether they are good or evil.

So. by becoming the Dark Lord, you are ushering in the age of Humanity and Mortal Man, and doing away with the age of Gods.

The Gods understand this, which is why they cling to the light (A theme rather prevalent in Anor Londo).

Another little piece of in game hints that make me think this is that Humanity (A generally good thing in the game) is black....dark... Hmmm....

So, all in all (TL;DR)
Lighting the Fire = Bad (For humanity) / Good (For Gods)
Becoming the Dark Lord = Good (For Humanity) / Bad (For Gods)

Note that the power of the gods is never once refered to as the Age of Light, or even light with a capital 'L' except in the intro-which may not be referring to the gods at all. Sunlight and lightning belong to Gwyn, not the gods as a whole-and he's referred to as the Lord of Sunlight, not simply 'Light'. I think the conflict is between Fire and Dark, not Light and Dark, regardless of what the intro insinuates.