A few months ago I stumbled upon a game wherein the goal is to guide an elephant from one side of the screen to a pipe; perhaps you have seen it:

This is the only level

Here's the rub: The rules change on every level. In order to do well you have to be quick to change your view of how the new virtual world works. That takes a flexible mind and accurate interpretation of the cues that the game gives you.

I sent this to some of my colleagues and have concluded anecdotally that their mental flexibility is in rough correlation with their results from the game. I think that experimental games are great and would, if done in a controlled setting, be an interesting way to evaluate mental acuity.