Oh definitely get one. There's are killer games by the bucket load-
Final Fantasy 3- 3D remake of a game that apparently didn't make it over here. Very old skool. Very good art direction and music.
Metroid Prime Hunters- online FPS, think Halo or Unreal Tournament (as they're quite basic too). Disposable single player and pretty addictive multiplayer.
Kirby Canvas Curse- a new take on the platform genre, only uses the touchscreen. It's quite old now but I keep finding myself going back to it for the unlockables, of which there are mountains of 'em.
New Mario and
Sonic Rush are apparently excellent returns for both games, though I find neither as good as their Mega Drive/SNES originals.
Tetris DS- online now. IMO the most immersive game. I have literally lost hours to this game without knowing, and missed my bus stop a fair few times.
Castlevania Dawn of Sorrow- IMO the best 2D game ever. RPG elements weaved well into a platformer with countless weapons, items and "souls". It's really epic and the music is just
phenomenal.
Mario Kart- best of the series so far. Plenty of modes and unlockables. It's old but there is always an army of people on WiFi.
Animal Crossing is pure addiction. Can get very repetative but it's such a charming, relaxing and beautifully made game.
Pokemon Pearl/Diamond- Super epic games, typical Pokemon run - great music, charming graphics. Add in WiFi and it's begging for 100-200 hour play times.
Advance Wars- a love/hate kind of game. TBS war game. I hear it can be very addictive.
Hotel Dusk- incredibly immersive story-based mystery game. Spiritual sequel to
Another Code.
Resident Evil is supposed to be good, couldn't get into it myself (spoilt by the Cube version
)