A classic triumph of substance over style, Square Enix take note!
In the unlikely event you've never heard of it, a variety of shapes (well, seven) fall from the top of the screen and it's your job to make solid "lines" out of them, in other words, without gaps or spaces. Do so, and the line disappears, and you score points. You can rotate the shapes so that they can be manipulated into gaps, and if you are able to complete four lines en masse, you score bonus points.
This is obviously sounding ridiculously simple and basic, yet equally ridiculous is the addictiveness of the game. Cups of tea are stone cold before you even notice, thinking "a quick go" won't turn into half an hour in the chase for higher scores. Start on a later difficulty level, and you are able to score even more highly.
Granted it won't win any prizes now, and up against the behemoths like Halo, Call of Duty and Final Fantasy, it has nothing to offer modern gaming, right?
Wrong. Tetris is a lesson for developers and gamers alike. It's an enduring message that style never wins out over substance, and a timely reminder that it doesn't matter how good it looks or how big a budget it had, enjoyable gameplay is everything.
In a world where games take years to be released after being announced and require voice actors, motion capture, and an advertising campaign that'd make the next Terminator movie look tame by comparison, the fact Tetris was created by a lone Russian programmer shows what can be achieved with dedication and a resolute ideal: make it fun. Still as enjoyable today as it ever was.