Really a nice game and a good variant of the "Puzzle Bobble (Bust a Move)" game-principle. Would it be possible, to realize a VERSUS mode and add CPU-players, against which the human player can compete then?
That would be great, especially if you had these CPU opponents in different selectable levels of difficulty. Puzzle Bobble style games are by far the most fun, when they are played against each other, but unfortunately you usually don't have any other human players at hand, so CPU-opponents would be really great to have.
Of course, the game-size then would be bigger than 4kbytes, when this would be added, but that wouldn't matter, cause a Deluxe Version of the game could follow the original 4kb version. :-)