I liked the art, but the gameplay... not so much. Which I'm sure you probably expected. It's a interesting concept, that's for sure. But, the controls are very clunky, the green gems sometimes get stuck in the walls if you shove them at a weird angle, and it can be very hard to tell where your tunnels are in the later levels.
First simple change I'd suggest is, make the background color of each stripping stage different from the one before it.
Also, this might be the opposite of simple, but you could make it so that jumping doesn't cause you to dig, just tie that to the down arrow. Or maybe, make digging be directional in some way? Like, there's a "dig" toggle, and while active, your movement will dig in the direction you're pressing.