At a basic level, the same sorts of games that work with the DS. RPGs did especially well with it.

Survival Horror could also work well, as a second screen lets you keep menus and inventories up, and we've already seen how tense those games can be when you can't pause during inventory changes.

I'd like to see an Aliens game. Dedicate the game pad screen to the motion detector, and build the xenomorph AI to use crawlspaces, vents, and ceilings and you have fantastic potential. If they didn't ruin it.