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the 'endless replayability' of tetris is a ruse. you would get sick of it and hit personal/human limits of play really quick.

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I can speak from personal experience that this is not true. The only reason I stopped playing Tetris is the pain it caused my wrists.

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it would be a lot easier to make creative 'sub-games' of mario 3 by doing stuff by setting certain goals or putting restrictions on your play actions.

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Sort of like beating the original Zelda without ever using a sword, except to finish off Ganon...