Not much of an improvement but still a blast.
Before I go into the bad I'll mention some of the good things of the game. For one, the combat is as great as it's ever been, if not better. Dismemberment of enemy limbs and the obliteration techniques are very satisfying to perform. Though without limbs, enemies are more dangerous requiring you to finish them off after they lose one or they'll grab you to do some serious damage. The weapon variety is decent and each has its own set of moves and you earn more as you upgrade. You regenerate a portion of your health after each fight though the amount you gain back is less as you gain more damage each battle. Save points are more frequent and will regenerate all of your health for your first save on each one. Boss fights are more frequent and you sometimes fight two bosses at the same time or one right after another. Ninja cinema is a great addition as well allowing you to upload your game play vids or download some to see how others play.
Now for the bad, after two remakes you'd figure Team Ninja will finally fix the one big flaw of the NG games, the BAD camera. Ninja Gaiden 2 doesn't make it better but worse. Team Ninja pulled it in closer which inhibits you even more than the previous games to see what's coming at you which leaves you vulnerable to enemies off screen. The level design is linear and has hardly any platforming that the original had and more closed in which makes the camera cooperate even less. Even though I praised the original and the remakes for testing gamers' skills with its difficulty, there's a fine line between difficult and just plain straight up cheap. Ninja Gaiden 2 made a turn for the worst with this by having some enemies constantly throw projectiles at you which some are unblockable (especially rockets) and will stop you in your tracks leaving you vulnerable to enemy attacks and grabs, especially of those off screen. The higher the difficulty the more projectiles are thrown at you.
If you can put up with some of the cheapness and a bad camera at times, it will be a bloody satisfying action game.