Through the magic of Augmented Reality you can make your 3DS Mii walk around your IRL environment. The pre-installed feature (I wouldn't call it a game) lets you move your Mii around, pose it and then take a 3D picture of it. This is fun for about two minutes total. Add in the Nintendo character cards, which have the same functionality, and my figures come out to about 12 total minutes of fun with the included software and cards.
Nah, I'm being too hard on it. This AR Mii stuff is pretty neat, and it's definitely good for showing off what your shiny new 3DS can do. Now let's see if I can get in on this naughty Peach positioning thing that everyone's into.