Very simple to understand and easy to play. Has room to expand on that toolset. Nicely designed!
I like that it was basically in a 64 x 64 res port too, which worked well functionally and visually and didn't take anything away from the game play.
The difficulty curve was a bit easy for the most part, I didn't really feel that challenged even after 6 or so levels (maybe down to level generation?). Maybe some more hazards would of helped. For example flooding, toxic graves, explosive gas etc. The water drop animation clues me in to what might be a tile that floods my tunnel any way.
Really nice little game! Just needs a tiny bit more challenge to keep it interesting over a long period,