Tetris is still a game that people play. (Read this excellent history and consideration of the game from Noah Davis.) It doesn't involve flinging bird-heads at fat pigs or shooting aliens with nuclear pistols or even trying to make a three-pointer with Monta Ellis. (The third option here is the least realistic.) It's just a bunch of blocks falling from the sky, and you have to stack them. But you know that; everyone knows that because everyone has played Tetris at some point. Seriously, at least one billion people are estimated to have played the block-arranging game.
Why, then? Why is such a simple game—a game without any talking dogs with heads of dragons or elves conquering forest colonies—so popular? It's sort of like a drug. From Wired in 1995:
In first-time users, Tetris significantly raises cerebral glucose metabolic rates (GMRs), meaning brain energy consumption soars. Yet, after four to eight weeks of daily doses, GMRs sink to normal, while performance increases seven-fold, on average. Tetris trains your brain to stop using inefficient gray matter, perhaps a key cognitive strategy for learning. In fact, the lowest final GMRs are found in the best players' brains, the ones most efficient at dealing with Tetris' Daedalian geometry.
The elevated GMR "high" is why you get wired after hours of play. Your old dog of a brain learns the Tetris trick by munching cerebral glucose. Neural hoop-jumping seems to be streamlined until performance peaks, and then your old dog stops craving Milkbones.
The Tetris effect is a biochemical, reductionistic metaphor, if you will, for curiosity, invention, the creative urge. To fit shapes together is to organize, to build, to make deals, to fix, to understand, to fold sheets. All of our mental activities are analogous, each as potentially addictive as the next.
From that story came the idea of the "Tetris Effect," which refers to the point at which something you devote a lot of time to (like playing Tetris) begins to take over your thoughts and mental images (dreaming of falling blocks). There's also recent research that suggests Tetris might even reduce the effects of PTSD in soldiers.
As Tom Stafford wrote for the BBC this past October, the game also taps into some human desires:
Tetris holds our attention by continually creating unfinished tasks. Each action in the game allows us to solve part of the puzzle, filling up a row or rows completely so that they disappear, but is also just as likely to create new, unfinished work. A chain of these partial-solutions and newly triggered unsolved tasks can easily stretch to hours, each moment full of the same kind of satisfaction as scratching an itch.
We play, according to Stafford, because we like to scratch those itches, we need to get everything organized, and we need to close every opening. But what if every opening couldn't be closed? And Tetris was just a never-ending loop of new blocks to be stacked? Someone at Digg posted a link to this: a Wikipedia-like Tetris page that explains how to make the game last forever. I can't understand it; I haven't played enough Tetris for my brain to ever function on that level, but there is at least one person (hint: the person who wrote it) who does.
To summarize: There is a Earth-wide-popular game that can give our brain a high and that grabs our attention by tapping into a desire to finish what's unfinished and get things organized. And there is also a way to make that game last forever. I'm not (yet) looking to achieve world-domination-by-mind-control, but if I was, I think I now know where I would start.