Dark Souls is like a high class, outrageously expensive dominatrix. She punishes you thoroughly. Then, when you're all finished, you shell out for more. That's what NG+ is all about. More punishment, but also more teeth-grinding, fist-pumping, screaming at the telly satisfaction. Starting an NG+ after finishing the main story, delivers you back to the Undead Asylum, only this time complete with your weapons, inventory (minus keys) and stats from the end of your first game.
Enemies are of course tougher, but as a result, the game experience is very different to the first play through. You easily glide through the first few hours like a vengeful god, before taking time to explore the fathomless depths of From Software's world. And therein lies the real joy of a second play though: the knowledge of what is up the road allows you to soak up the detail, instead of cower the shadows, edging round every last corner.