Not many games out there are very pen-friendly. Here's one that was not designed for the pen, but it works brilliantly. Escapa! is incredibly simple - just move the red block so that it doesn't touch any of the moving blue blocks or the walls. That's it, except that the blocks speed up and move randomly. Highly addictive! It's web-based and free.

According to the site, if you can get to 18 seconds you're doing well. I hit 18.5 seconds - let's see how you do!