Tombed plays like a game you might have found in the arcade, circa 1982. By that I don't mean the graphics alone, which are indeed retro and pixelated, but the feeling of the gameplay as well. The theme of the competition was "onrushing wall of doom," and you play Danger Jane in a Indiana Jones-like action sequence: spikes are falling downward, and you must dig down through the tomb to keep ahead of oncoming death. This means moving left and right through undiggable rock, using Shift to dig through colored square regions, and, well, a few other tricks you'll figure out soon enough.
The reason it feels so arcade-like is that the timing of each level is carefully planned so that you can get through it without dying just barely; near-optimal play is required, and you will often die multiple times in a level before progressing to the next. "Levels" last mere seconds here, and continues are from the beginning of the level, thankfully.
All it needs to be an arcade game is a high score list, three lives, and continues for an additional quarter.
As it is, if you like this kind of gameplay, watch out for the carpal tunnel -- it's both addictive enough and fast enough that you will be absolutely hammering at the keys.