In a 1up interview, Atari's Tavit Geudelekian described the level-sharing capabilities of the DS and PSP versions of N+: "the DS and PSP [versions] will support a full level editor that will allow players to build their own stages and share them locally via ad hoc connection or upload them through an infrastructure connection to a database of user-created levels online."
Unfortunately, because the DS lacks any kind of permanent storage, you'll only be able to download a few levels at a time, and they'll be lost when you turn the system off. We'd love to see the interface for designing levels, but none of the three new screens of the DS version highlight that feature.
N+ features a Pure mode, which is a direct port of the PC version, and a Plus mode, with new graphics and enemies. Also new to the handheld remakes: multiplayer, in both cooperative and competitive modes!