You see this is one of those times where i can be a stuck up ass hole and be like, "haha silly people, I played this game before it got popular. So there for i am superior"
Mine craft used to be a game where you could either limitedly built whatever the hell you wanted in a small space with as many blocks as you want, or you could so survival where you had to work a little harder to get stuff and there "mobs" of enemies that could kill you in your little blocky vulnerability.
Now Notch (the creator) has become basically GOD! he has turned that small little game into one of thee funnest games I have played in a while (he made the level generator generate your playing field to be 8 times the surface of the earth.. im pretty sure), and it's uniqueness comes from the complex simplicity of it.
you do in fact mine and craft as the primary goal, but once you get really good you can start to make grand structures. for example a friend of mine is building a 1 to 1 scale model of the Parthenon (no im not shitting you)
I highly recommend this game to anyone who is considering/not considering giving it a try
and if you buy it before he comes out with Beta it is only 12 bucks, but if you wait to long it will be 24... so give it a try, buy it, play it, love it and in general be a more awesome person... in case you can't tell I LOVE MINECRAFT!