A tile-based puzzle game, where a sequence of blocks fall into the game area, and must be matched into a line in order to score points/clear the blocks.
The original game was in 2D, with a 10 wide and 20 tall playing area. It consited of 7 different tetriminos (blocks) - each was made up of a different arrangement of 4 1x1 blocks.
To clear a line, each of the 10 spaces on that line needed to contain some part of a solid block. Additional points were awarded for clearing multiple lines consecutively.
The game ended when you placed a tetromino above the 20th level of the playing area.