Great action. Smooth graphics. And ninjas. What else do you need?
NGDS has awesome 3D graphics - probably some of the best of the DS. Every model in the game is in 3D, which would normally put some pressure on the DS. This is overcome by making the backgrounds 2D. This was a good move, but it presents some problems - there's no sense of interaction with the environment. Every fight in the game is always on an empty field, except for the odd few. It would have been awesome to have been able to fight enemies on separate floors of the same battlefield. Also, the set background fixes the camera, making some fights boil down to random scratching, because you can't see your character.
The combat is a lot of fun. Slashing across enemies allows you (Ryu Hayabusa) to attack them with your sword, allowing you to chain sword combos. Tapping rapidly shoots Ryu's equipped ranged weapon. Jumping into the air allows for a few aerial combos. Scratching the screen allows for a charged attack. This seems like a large move list, but after a couple of hours the combat starts to get repetitive. As mentioned before, almost every fight plays out in the same way. Enemy variety is also somewhat lacking.
There are a lot of enemies in this game. They all look awesome. They make satisfying cries of pain as you cut their pitiful lives with your devastating blade. But sooner or later, you realise that all of the enemies are prety much the same. There are a few main categories of enemies. One is the ground troop, which is chucked into fights as something nice and easy to kill. There are also heavier, more dangerous ground troops, who don't flinch from your attacks. There are floating, ranged enemies, and ranged troops on the ground. Ground troops never go into the air (unless you take them there). The game would have been much more fun if melee troops could jump into the air, and if they had a larger variety of attacks. Most enemies only have one or two different attacks, and many enemies have the same attack, just looking different. This kills the variety.
Not only do the repetitive battles kill the joy after a few hours, they also make the game too easy. Once you figure out a single strategy, you can implement across the whole game. The bosses, however, add a bit of extra spice. Though they look awesome, only a few of them are actually that much of a challenge. However, they're still a hell of a lot of fun to kill.
The main problems with this game is difficulty and length. Normal mode can be blasted through in about 6 hours, and the hard mode isn't actually all that challenging either, and only doubles the play time. It's also much too linear, so there's no room for different playthroughs. However, if you still want top notch action, and you don't mind just a little bit of repetitiveness, pick this one up.