The game is basically N, on the DS, with new levels. That's really all it needs to be -- there are no Touch!! minigames or training exercises. David told me that the physics were all in place with the exception of the ragdoll explosions, but when I died (a bunch of times) I fell into a pile of limbs just fine.
The view for the DS game provides a zoomed-in bottom screen and a zoomed-out view of the whole level on the top screen. It's actually a pretty elegant solution to the low (relative to the PC) resolution of the DS, and allowed me to focus on tiny platforming setpieces while keeping an eye on the enemies floating around the level. The enemies at this point were some round blue obstacles that wandered around the levels. David promised a bunch of all-new enemies in the game's Plus mode.
The game will feature all new levels designed by original creators Metanet in both its Pure (based on the original Flash game) and Plus (new graphics and enemies) versions. Both the DS and PSP versions contain new soundtracks by an artist called 5Limbs, though I didn't hear any of this. Also seen but not truly experienced is the NED level editor, which, on the DS, will be stylus-controlled, and will have both ad-hoc and online level sharing.
The level I played was a wall-jumping exercise in which my ninja ran down long straightaways, then jumped into a wall containing coins, opposite another wall filled with tiny red mines. The run-jump-run-jump had a brilliant rhythm to it reminiscent of a good Sonic level (if you can remember such a thing.) Any version of N+ seems like a good bet for high-speed platforming, and the DS version is in no way scaled back. In fact, the level editor may make it the N+ of choice.