Fire Emblem Awakening: Do it. Just do it.
Luigi's Mansion 2: Not played it myself yet, but I've heard nothing but awesome things about it, and it's one of the fastest selling games for 3DS, so there doesn't seem much reason to not go for it.
Super Mario 3D Land: Yes, it's another Mario game. But it's also the highest selling 3DS game for a reason. You don't get 3D platformers as tightly designed an put together as this. The first half is a bit simple by normal Mario standards, but the latter half of the game is incredible.
ResonanceSD said:
Zero Escape: Virtue's Last Reward
Fire Emblem: Awakening
That's it, all the rest is not worth your time or money
So out of a library of dozens and dozens of games, those two are the
only ones worth playing? Not Etrian Odyssey IV? Not Soul Hackers? Not Luigi's Mansion? Because I think most other people would agree that at this point, the 3DS is building up one heck of a kickass library of games.