Yeah, it's pretty amazing, and completely addictive for a week or two, with the potential for part-time fun for months
Zero Punctuation review--amusing and informative ;D
Basically it's a pixel block world with very simplistic and bright graphics (stylized, not "bad"). You start off clueless, dumped into wilderness, and explore a bit; then night falls and monsters spawn in any unlit
area (some of which are killed again by sunlight). As you survive, you find out that there's a massive crafting system with tons of resources both in the overworld and in caves beneath the ground. You set your own goals--make a castle, or a massive walled-in brightly-lit farm, or whatever
My multi-player server is currently excavating, forming and decorating a HUGE underground cave system into a giant underground city termed by my WoW guildmate, amusingly enough, as the Undercity >.<