Board Thread:Lore Discussion/@comment-172.56.9.225-20140731112048/@comment-5264386-20140731120116

Basically, the two endings represent the two different Ages presented to you within the lore of Dark Souls. If you choose to kindle the First Flame, then you are (supposedly) extending the Age of Fire - or rather, the Age of the Gods. Alternatively, if you choose to leave the Kiln instead, you are denouncing the Lords, and you (supposedly) begin the Age of Dark - the Age of Man, according to Kaathe.

However, the reason I say supposedly in the description of both endings is because we don't actually get to see what happens after we make our choice. We don't know how long we extend the Age of Fire for if we kindled the First Flame, and we certainly don't know if the Age of Dark truly is the "Age of Man". In both scenarios, we also don't know if the curse of Undeath is cured or not. As a result, it's fairly hard to put a definitive "this ending is the 'good' one, whilst that one is the 'bad' one" label on the endings, as there are different ways of interpreting them.