A worthy sequel
Ninja Gaiden 2 uses the same gameplay mechanics as the first games, so this is basically the same as the first game with more levels and a different story. The sound effects are practically the same as the first game, but the music has gotten much better which helps when you are playing a level repeatedly. The difficulty is still here but it is hard to say if it is more challenging than Ninja Gaiden 1.
This game is extremely difficult and while that isn't a bad thing for people who are up for the challenge, it is also long for a game like this. Also, timing is a crucial factor and unless you master it, you'll be pulling your hair out because you can beat one jump that you've tried to for 10 minutes(or more!).
The Bottom Line
Very hard, long, and low replayability. Other than those factors, its a great game to play.