What is Minecraft?What is Minecraft?
Minecraft is a game about squares.
In a world made of blocks, you (a rather blocky person yourself) must use your wits and common sense to build and carve a way to safety. This is a dangerous world, make no mistake ? monsters appear from out of the dark, mountains themselves can roar at you, and an errant poke in the wrong direction could bury you alive under tons of soil.
But all is not lost. You?re a smart adventurer, after all. After tearing down some trees with your bare hands and building yourself a rudimentary shelter, you?ll begin to explore the mineral wealth of this new land ? iron, coal, gold, and even stranger treasures await you deep in the cores of these mountains. The question is, can you work your way to the heart of the earth, plunder its riches, and return to tell the tale?
Developed by one-man creator Markus Persson (also known as Notch), Minecraft is a Java-based, sandbox-style adventure. It fits squarely among more difficult survival games such as Dwarf Fortress and NetHack, while keeping the simple charm of one?s younger building-block days. It is outwardly simple, internally complex, easy to play, and difficult to master. Perhaps best of all, despite being constructed of laughable square blocks, the game manages to deliver a wonderful atmosphere of fear, paranoia, determination, and reward all in one package.
There are 2 game modes, Creative and Survival.
Creative is basically digital Lego. No restictions, no tools required. Just build. You can create some really cool stuff here.

... Or just copy sprites, I don't really care.

Either way, the real meat of the game is in Survival mode. I'll just copy paste a description someone else made.
Survival is a near-perfect example of what we hope developers mean when they start talking about "emergent gameplay." Beginning with nothing but the ability to punch the hell out of things in a variably hostile and procedurally generated world, you can with a little effort and luck and time build something worth bragging about to your disinterested family and friends. Build a house or a lake or a farm or a subterranean lava maze, brick by fucking brick. Hunt spiders for thread. Kill pigs for delicious ham. Master the red flower. Run out of torches so far beneath the earth that digging upwards in a panic is as likely to get you a face full of lava as it is to get you a face full of ocean. Build shit no one else has ever built in places no one else has ever been.
And if that isn't enough, how about a recommendation from VALVE?
This afternoon Corey Peters suddenly yelped and jumped out of his chair claiming that a Creeper had gotten into the new training map he was working on and that it was blocking his ability to get any work done. This was followed a few minutes later by Jon Lippincott claiming he couldn't finish up his code because he had run out of Iron Ore. Even as I write this I can hear Dave Riller telling a story about how he beat a sheep to death with his bare hands to make a new set of pants and a woolly hat...
...In Minecraft you carve out your own little empire in the wild, building just about whatever you want while the natural world tries to slaughter you every nightfall. The game's box-like representation of reality is cute and definitely charming...until a horde of cute box-like skeletons rip your cute little box-like arms from your cute little box-like body in a spray of cute little box-like blood and gore.
Also, Infinite terrain, well not quite infinite, but 8 TIMES THE SURFACE AREA OF THE EARTH. It will procedurally generate new and interesting terrain. You'll be amazed by some of the stuff this game makes.
Is it free? yes and no... Creative is free, but Survival is pay only. however, the game is still in alpha and is about 12 dollars right now. Once the game goes into Beta the price will double so get it while it's cheap! Seriously, this much entertainment for that much cash seems like thievery.
Go check it out!