Kid Icarus Uprising is bloody fantastic holy shit. Also already recommended is of course Tales of the Abyss 3D, if you haven't played the original TotA (It's just a port, so there's really nothing new offered if you played the original).
Samurai Warriors Chronicles also isn't halfbad. For games running on the "old" Musou engine (DW games up to 5, SW series), it's actually really really solid and inventive for a Musou game. It was my favourite for a while.
If you have access to a 3DS Prepaid card or credit card, try getting Pushmo off of the Nintendo eShop. It's a fantastic little puzzle game with a simplistic nature that turns out to be incredibly complex in practice, that has a very active stage creating community right now.
Also, Resident Evil Uprising basically combines 4/5's controls with the atmosphere of the older games. It's genuinely creepy and makes you feel really threatened, it's very difficult, and the bonus (absolutely huge) mode that can be played single-player or multiplayer is an absolute blast that puts Mercenaries modes in the previous games to shame. My roommate had pretty much lost faith in the series, but he has loved Uprising to pieces and I can completely see why.
Also, Mario Kart 7 and Super Mario Land 3D are both great games in their own right too; how the heck did I forget them?
