Pieces will come in from all four directions! Complete a "ring" around the middle to clear pieces and cascade them towards the center. Use the following keys to play:
Arrow Keys: slide pieces up/down/left/right, or fast fall towards center
Left Ctrl / Alt: Rotate current piece counter-clockwise / clockwise.
Enter: Swap the held piece (shown in upper left) with the current piece on the board.
Some example gameplay