Just bought a 3DS - which games should I get?

Pokemon X/Y

New Super Mario Bros. 2

Animal Crossing New Leaf

Fire Emblem Awakening

Go to Best Buy, there is a Buy One Get One Free sale on select titles, mostly good first party Nintendo titles.

POKEEMAN X OR Y

OR BOTH

fist try to get an R4 card
The rest..well you know already

You should try the demo for tomodachi life.
Either you'll love the game, or hate it.
It is a bit repetitive, but the premise is simply too awesome.
Also, buy Mario Kart 7, a link between worlds. There is no way of not liking those.
If you are into JRPGs, 3DS has a lot of good ones.
Buy Smash Bros when it comes out.

just got one like 10min ago, 3ds excel