Metanet's N is a game in which the player is tasked with running very quickly through obstacles and jumping with high levels of precision in order to reach the exit door. It takes place in small, self-contained levels, uses simple, clean graphics, and has no real story to remember.
Though it first appeared as a freeware PC game and was then remade and enhanced as an Xbox Live Arcade game, there is no denying that N is an ideal handheld game. You really couldn't come up with a better design for an on-the-go game.
N+ from Atari is basically N, on the DS, with new levels. So, naturally, it works out pretty well.