We now have written a reasonably complete, reasonably fun game of Tetris.  Congratulations!
 

That said, our game is somewhat minimalist, leaving many opportunities for additional work by your students.  Here are some ideas:

• A "Pause" feature;

• Dual rotation (adding clockwise rotation in addition to counterclockwise rotation);

• Hard drop:  hitting a key (such as space bar) immediately drops a piece as far as it can go and places it on the board;

• "Splash screens" with help instructions;

• More attractive pieces (look into Graphics2D for some interesting options);

• Piece Preview (so you can see what the next piece will be before it arrives);

• Levels of play with increasing difficulty (dropping faster, with more difficult piece types, and with some cells randomly filled, etc);

• High scores list (even better:  stored on the web and shared across users);

• Integration with Swing widgets (buttons, menus, etc);

• Making this implementation more object-oriented (seeing as it basically isn't at this point) -- for example, adding an abstract Piece class with LPiece, SPiece, and so on as subclasses, and then actual falling pieces as instances;

• A Piece editor (so you can create new types of pieces); and

• Network-based multiplayer versions.
   

Enjoy!!!