Classic Mining game.
I spent many hours playing this game. I have always enjoyed mining games like this one. However I wish there were an ending, as to add some replayability. And although the beginning was possible to get through, it was far too tedious, fuel prices did seem a little too inflated early game. In the future perhaps have the first few drill types require a cheaper fuel, and more advanced models a more expensive fuel to help with this issue.
I'd also like to note a bug I encountered, which is just as frustrating as it is unfortunate. I have cleared every single block on the map, including the hidden column on the far right, but I only ended up with 9 out of 10 of the Giant Gems, so I was unable to get the last Medal(achievement).
For some minor issues and a unfortunate, but seemingly not consistant bug. I rate the game a 4/5, 9/10