I have to admit, I’ve never actually run this role play with students. But I’ve done it with other teachers, and while acting out what the computer does can feel painfully slow, it really does emphasize the passing of control (and in some cases, variables) from one object to another.
The other GridWorld thing I’m excited about right now is a competition I’m running in my AP class to make a Critter with the best Rock-Paper-Scissors playing strategy. It’s written up — with all the files available for you to download should you wish to run it in your own classroom — on my school web site. I did it last year and came up with a few tweaks and changes based on that experience that I think will improve things this time around. At a minimum you should at least play some Rock-Paper-Scissors against the New York Times robot.