The controls are basic - directional pad to move and X to jump - but getting used to how your ninja self moves takes some getting used to. At first it feels like the little guy has way too much weight and inertia for his diminutive size; changing directions feels sluggish, and if you're running downhill too fast he'll have a hard time jumping at all.
Once you get used to the floaty controls though, they actually add to the game's puzzle/cerebral element. You'll need to think out your paths carefully and consider the game's unique physics to avoid ending up as a pulpy pile on the floor. That said, prepare to die frequently (like every ten seconds frequently), because the moment you start to get comfortable, the difficulty gets ramped up another notch. And don't worry, dying isn't such a big deal when each level can be completed in under 30 seconds. If anything, it just adds to your accomplishment when you actually do make it through a tough spot after the 20th attempt.
It may be difficult to justify buying a game that alreadyexists for free on the web, but at least Atari picked a really good free game to port. The episodic format also lends itself to playing on-the-go, so there's at least some value in being able to haul N+ along during your commute. Still, we'll have to see whether the added multiplayer (both co-op and versus), community features, and level editor (quite the rage these days) are enough to set it apart from its flash-based brother when N+ hits this March.