Nintendo 3DS

Obviously depends on what you're into, but my favorite 3DS game is Etrian Odyssey. It's a dungeon crawler RPG about exploring Yggdrasil and contains a lot of Norse mythology. There are the original series and then the "untold" versions which adds more characters, dialogue, and overall better graphics but unfortunately not every game got an untold version. 

bravely default is a MUST if you like rpg's. highly highly recommend it

a few others i personally recommend: fire emblem awakening, kirby triple deluxe/kirby planet robobot, tomodachi life, persona q/q2, monster hunter 4 ultimate, any of the zeldas, and final fantasy explorers which is a hidden gem imho

If you're like me and love making Miis then I gotta obviously shout out Tomodachi Life. Miitopia as well if you haven't had a chance to play the Switch version.

Rhythm Heaven Megamix, All the Phoenix Wright games, Ikachan is a fun little game.

The game I would recommend is Warioware Gold. It's not a long game by a long shot but it's good and simple fun.

You've got to play Kid Icarus Uprising. Its one of the best games on the entire system. Masahiro Sakurai made an entire studio just to reboot the Kid Icarus franchise and then never did anything with it again. And if you have the patience for an RPG I'd highly recommend Shin Megami Tensei IV

Tomodachi life, Kirby extra epic yarn and super mario 3d world. Those are very fun. I would also get a zelda game for it.

I'm gonna recommend a hidden gem- Rhythm Thief: The Emperor's Treasure.

The early 3DS' life had a lot of strange third party games that sadly waned in the later years, but this one is pure SEGA goodness distilled into one package.