Homestarrunner.com did an amusing parody of NinjaGaiden's opening cutscene on April Fools day, 2004.
There was also a NinjaGaiden game for the GameBoy, but it's not really worth playing; it once had an entirely different plot and set of characters, but since the original wasn't selling well, they slapped some NG sprites on it.
And finally, there's the XBox game, where Ryu sets out to get revenge against the demons that destroyed his home village. At times the plot feels like the game makers made a bunch of cutscenes and then built a story around them:
scene: a military railroad base. Two soldiers patrol the area. Suddenly the ground rumbles, and a train engine bursts through one of the doors. The soldiers dive for cover, and the camera zooms in on the conductor's booth, where a NINJA is driving!
But anyway the gameplay certainly doesn't suffer. NinjaGaiden for XBox is a 3D platformer done right. Ryu can run up or along walls, roll and flip, swing from convenient bars, and perform a huge number of attacks with such weapons as: the ninja sword, the nunchaku, the bladed nunchaku (also known as kama or "Vigoorian Flails" in the game), the big sword, the wooden sword, the oar, and the demonic sword. He also gets shuriken and a bow for missile attacks, and of course Ninpo for magical attacks. In play, the game looks a bit like PrinceOfPersia would look if the emphasis were more on combat than on platform puzzles. And with ninjas and demons instead of possessed castle guards. And of course, it's hard. Not quite as hard as the original NinjaGaiden, but close, and it has harder difficulty levels. And if you're feeling particularly masochistic, you can always play with only using the wooden sword.
Let people who have played the game more fill in content here. NeedsRewriting.
This game is great because you never run out of moments to stare in awe at what you just did, and yell out "I am ninja!" The hand-to-hand combat model is way more advanced than simply "hit X to swing, this weapon does more damage." Each of the weapons has a significant number of moves available to it, much like a fighting game, and with this game's learning curve, you actually do need to think about what you're doing because button-mashing won't work beyond maybe three levels. What will work, though, is doing a front-flip over a guy, grabbing him by the neck at the midpoint, throwing him over you (Guillotine Throw is my favorite move), rolling forward, doing a jumping forward slash for the decapitation on the second guy, and pulling the slash-slash-impale combo on the third.
The story on this game is utterly useless, but the gameplay is so phenomenal that it makes up for it entirely. JamesOsburn should have it on his XBox as soon as it gets modded again (soon), and then we can get the first expansion pack, Hurricane Pack Vol. 1, which includes no levels, but new enemies, a quarterstaff, and new techniques like interceptions and essence-less ultimate attacks. Oh, that reminds me, watching an ultimate attack is a cinematic experience to make you shit yourself the first time around because it's so damn cool.
The game is also notable for the old man in the shop who sounds like he's in a porno. "Ohhh, scarab." - ask anyone who's played this to repeat this line for you in the required voice and you will be amused.