Unfortunately, the game fails in many areas. First, it's a multiplayer game that requires only one calculator. Those games by nature are terrible to play with impossible controls. The routines in ZTetris make it very easy to do. The controls are also very strange.
Random keys seem to do random things.
I assume this is a bug. Another problem is the graphics. It is far from impossible to make a decent 8x8 sprite. The walls are drawn well enough. I did notice another small bug.