Metroid Series
The DS has so far not been home to many Metroid games, but since all those which are on the DS are great games to play, they shall be listed here.
Metroid Prime Hunters Demo
This demo came free with the DS, and is quite a good game. While nowhere near the high quality of the real game, and not anywhere near as long, it is a relatively enjoyable game. There are three single player modes, with one requiring you simply to survive an onslaught of monsters, one requiring you to reach the end of a laboratory based area and defeat a boss and one requiring you to collect small orbs in Morph Ball form. There is also a limited multiplayer mode for up to four players.
Metroid Prime Pinball
I personally do not know much about this game, other than it is a kind of different pinball game to the normal kind, and has Metroid themed tables and enemies from the series on the board, which you can defeat for more points.