I think Dark Souls is both about the futility and beauty of life. The game focuses on hard, punishing gameplay and life, similarly is punishing. One thing Dark Souls does, though is give a sense of satisfaction, you try so hard to make it somewhere or to overcome obstacles that, when you do so, you feel relieved. This is similar to how events in one's life may seem, made up of little instances of difficulty, then (if you try hard enough) success. Although the overall story of Dark Souls is not such a positive message, I believe the story for the souls series has a much darker outlook on life. The souls series, in my opinion portrays a message expressing the futility of life. The souls series tries to deliver a message that says: No matter how much you overcome, no matter how many good times you've had, and no matter how many times you solve every problem, more will surface. I believe the cycle of light and dark in the souls series symbolizes not only the futility of life, but also the beauty and perseverance of life. No matter how many times things fall into darkness, light will always return and visa-versa.
"All men trust fully the illusion of life. But is this so wrong? A construction, a facade, and yet... A world full of warmth and resplendence." - Aldia