Non-minecraft post, however you must check this game out.
It is a free 3D game that uses infinite procedurally generated terrain, in which you can edit the landscape and gain resources, all set on a planet in outer-space where the enemies are aliens. Again, it is FREE.
This is only the FIRST release of the game ever, so it is sketchy. The developers have said that it isn’t optimised so only good computers will run it well at the moment, however you have nothing to lose by trying it.