Simple yet fun
Basically it's one of those "puzzle games" that doesn't feel like a "puzzle game." You play as Mr.Driller (big suprise) and you basically just drill your way down without getting crushed and surviving on oxygen. It sounds easy, but it really is. Yah, it's simple and it gets more simple as the game goes on since it isn't overly complex and it doesn't throw new things at you.
Even still, it's a good game, it's simple and fun but beyond that, don't expect much.