I play games on my Nintendo 3DS pretty often. Some games are better suited to portable systems, and the 3DS has a few features completely unique to it.
Maybe my favorite of these is called StreetPass. When your 3DS is off, in your pocket or backpack or wherever, it periodically sends out a ping using its wireless radio. If there is another 3DS in range, it will receive that ping, the two systems will exchange data, and a little green light on the top of the 3DS will light up to tell me I’ve StreetPassed with someone.