Kid Icarus Uprising and Mario Kart 7 are both great multiplayer games. I have never played Super Mario 3D land but I would assume that it is a grezt game as are most Mario games. The Legend of Zelda Ocarina of Time is an amazing game as well with some really nice graphics. Another amazing game is Resident Evil Revelations which has both amazing gameplay and graphics. Lastly, if you like fighting games I reccomend Super Street Fighter IV 3D Edition.
CRUSH3D is a brilliant puzzler, I love its quirky gameplay. Starfox 64 3D, Shinobi and Ghost Recon Shadow Wars offer a good challenge. You can't go wrong with these 4 unique titles.
There are a lot of really great games on the 3ds ( I own about 10 games for it as of right now) but There are a few stand-out titles that you should purchase.
Mario Kart 7
Kid Icarus Uprising
Resident evil Revelations
Super Mario 3d Land
You cannot go wrong with any of the games on this list!
Kid Icarus Uprising is the only one I have on cartridge, and it's awesome. I'd reccomend it, as well as Ocarina of Time 3D, since I've played that on N64. Other than that, both Monster Hunter games look good, as well as Tales of the Abyss and the Adventure Time game.
mariokart 7, mario and sonic at the london 2012 olympics and mario 3dland are my reccommendations as well as mario vs donkey kong minis march again on 3DSIware (combination of eshop and dsiware