Persona 3 Portable - It's Persona 3, with better writing for the new Female main character.

Golden Sun: Dark Dawn - Not as good as Golden Sun or Golden Sun: The Lost Age, but still a solid little game.

Pokémon Platinum - Best Pokémon game. Possibly beaten out by X and Y, but this thing blows the new ones away in terms of story and characterization.

Rune Factory 3 - The best of the Rune Factory series so far. It's Harvest Moon, with combat and a plot. Awesome, awesome game. I have put in hundreds of hours, and still have more left to do. One of the most underrated titles for the DS.

The World Ends With You - I hate the gameplay, but I love the story and world. Solid little game.

Final Fantasy Tactics A2: Grimoire of the Rift - Main story is lackluster, but the rest of the game makes up for it.