You get a drill, a minor backstory and at times new story-elements, but otherwise you dig to reach deeper, to the core of the planet.
And it is fun!
NOTE: it IS possible to beat the final possible level. The possible nuber of items on you is actualy infinite, you cankeep score on 'em manualy. If you mine enough, and buy enough amount of stuff, the fact that the later levels exponentialy rise the prices thus by time makes you unable to buy more items can be circumnavigated.
This is a challenge!