I recently bought a Japanese 3DS and man, that eShop is good. From Sega 3D Classics such as OutRun and Fantasy Zone to Virtual Console releases like Trip World and Joy Mecha Fight, there is a ton of great stuff there that just isn’t available on the North American eShop.
Although you can apparently use foreign credit cards on the Japanese eShop, the actual Japanese point cards are way more fun. Here are some that I’ve bought:
Kirby Fighters Z game download code (810 yen):
Regular point cards: