Mariokart DS is epic. Fully 3d, all the items and more, full fledged 4 cups with 4 or 5 races a piece, then 4 full cups from the previous Mariokarts (snes, gba, n64m gamecube). Online mode, DSvsDS, bots, battle modes. This game really blew me away.
New MarioBros game is really well done too. Tetris has a ton of modes. Rocketslime is another really done game.