Zelda and Super Paper Mario are the two biggest games right now. I'd get them if I were you.
Other two are kind of iffy, many other good games but no straight answers.
Wario Ware - corny, fast-paced, multi-player fun
Excite Truck - fast-paced, high flying racer but no dept and lame multi-player
Godfather - subpar GTA game basicaly, good enough for now though
Madden 07 - for Madden fans
Monkey Ball - most mini-games fail but the single-player is good if you like MB
SSX Blur - Same SSX but less character interaction (dulls it)
Elebits - great controls, good game, gets boring and repetitive