Guess the Correlation is a very simple game indeed: Look at a scatter plot, guess the correlation coefficient, win or lose. Are you mathematically minded enough to take on the challenge? Get close to the answer and you win a life; get it wrong and you lose one. It really is that simple: There are no amusing data sets, no trick questions, no distractions (unless you count the 8-bit soundtrack). Just a simple test of your ability to spot a trend.
But despite its simplicity, it's incredibly compelling. "Is that closer to an R-value of 0.7 or 0.65," you'll ask yourself. And then you'll play for minutes or hours. How strong is the correlation between your geekiness and the amount of time you spend playing it? Probably around R=0.78* or so.
* That is a made up R-value, sorry.