Minecraft hardcore mode teased. When you die, the world dies with you
This rule was the driving force behind Tom's Minecraft Experiment. With every death, he deleted that randomly generated world and got Minecraft to build a new one. Numerous updates have been made since the diary was written. Varied biomes, major geographical features like rivers and ravines and NPC villages will make it more painful to destroy Minecraft's increasingly distinct worlds. Hardcore mode won't let your petty human emotions get in the way. When you die, the world dies with you.
The world might not be the only casualty. Notch gave us the first details on Minecraft's XP system, and told us that he's experimenting with permadeath as part of the Adventure Update. “I’m a big roguelike fan,” Notch explained. “It’s really fun. The idea is that you level up really, really fast. You can grind away and level up fast if you want to, or you can just play as normal and level up that way. The longer you play, the bigger the risk of dying becomes. It’s the part that really works."
If you enjoy the thrill of pure exploration and like the idea of striking out into an unfamiliar wilderness until an Enderman eats you, then hardcore mode should be a great edition. Hopefully we'll see it soon as part of the recent spate of Adventure Update patches. The most recent, the Minecraft 1.9 pre-release, added big-nosed NPC villagers that inhabit the new NPC towns.