The object of the game is to locate rectangles on the play field by clicking each of four corners of the same color. The corner blocks go away and your score is increased by the number of blocks contained in the rectangle. When there are no more blocks in the top row, a new row of blocks fall replenishing the field.
Update: A new feature that Tonypa just added to the game is the bar below the play field that fills up as you clear rectangles. Once filled, a new color is added to the mix of colored blocks that drop into play, thereby reducing the possible combinations of rectangles available.
A good strategy is to clear the top row as quickly as possible to keep the field as filled as possible. NeliNurk is an excellent game design that is simple, elegant, and one that requires some strategic planning.
Tonypa is a Flash game designer who has contributed much to the development community. His tile-based game tutorials in Flash are some of the best that is available on the subject, and he recently added a new set tutorials on using vectors in Flash.