The Ninja Gaiden series is probably the best ninja series of the 1990s, and some of the finest action games ever.  Of the three that were made, Ninja Gaiden 2 is probably the best (and it's better on the NES than the SNES Ninja Gaiden Trilogy remake bundle.  Ninja Gaiden plays like castlevania after Simon Belmont has been trained in the ways of the Ninja, bouncing off walls and taking down relentlessly-spawning speedy baddies from all directions, and it presents the action amidst high qualtiy, meaningful and often moving cutscenes that tell the story of the Ninja Dude and his friends trying to stop evil punks from bringing a demon God back to life.  

Ryu Hayabusa runs from left to right, swording monsters and collecting powerups hidden in floating lanterns (on in the case of NG2 the sequel in floating red orbs).  He can spring special moves he collects into action by pressing up and attack for the price of some of his Ninja ammo that can be found in the red orbs (like all the other items the game has to offer).  Ryu can stick to and bounce off walls, and in this one he can climb for the first time (in the first game he could only climb when he was clinging to a ladder, otherwise he could only climb walls by awkwardly jumping off the wall and u-turning mid air and grabbing on to the wall slightly higher than he grabbed it in the first place--luckily this maneuver is never required and highly advantageous in only like one or two spots).  At the end of each level is a boss fight--like in Castlevania, Ryu dies when his Castlevania energy bar reaches zero, and the boss dies when the boss's "enemy" bar reaches zero--this is an "imitation is the sincerest form of flattery" situation, because while the play control, item distribution, item ammunition, energy bars and boss-battle-format seem lifted directly from the first Castlevania game, Ninja Gaiden shakes up enough of the play control and the feel of the game, and the presentation (such as the cutscenes) that Ninja Gaiden feels entirely like it's its own kind of thing, rather than a ripoff or clone.  

The biggest addition, gameplay-wise, over the first game are these phantom-doubles, red clones (you can collect up to two) who follow the hero around.  If he stops, they stop, even if they are in the air, and most importantly they attack when he does in the way he does, giving the hero the potential of a triple-shot special weapon deployment.  

It's hard to say if the plot of the second game is BETTER than the first game, but it's just different enough that a strong case can be made either way, the fact that it at least comes close is quite an accomplishment.  Difficulty-wise, Ninja Gaiden 2 eliminated some viciously-difficult platforming bits from the final stages of the first game making completing the game a bit closer and a little less frustrating to achieve.  

By comparison, Ninja Gaiden 3 had the chance to be comparably good.  It was designed with the idea that it should be possible and not insanely difficult, so the hero was given a collectable sword upgrade and a more forgiving "floaty" jump, and things were on their way to turning out well, but some idiot in the United States decided to make every enemy do twice as much damage as intended, they removed the health-up potions, they removed check points so players must backtrack miles when they die and for the first time they put a limit on the number of continues (5 max).  This makes me really angry, it is a crime against humanity and it is yet another example of why piracy is morally justified, so feel free to download the japanese ROM if you want to play the real game (just like downloading the original star wars trilogy, prior to george lucas pooping on it, is not illegal because no legitimate government would frown on the act).  

But I digress... as it was released, the third Ninja Gaiden game is so idiotically difficult that there is only really competition between NG1 and NG2, and NG2 is probably the best of the two because of the additional special weapons, the awesome addition of the phantom doubles (which don't return in NG3 btw), and also there is the addition of environmental annoyances, such as levels in which the wind changes direction and messes with you, levels where the surfaces are icy, levels where there are water currents that push you around, levels that are mostly pitch black except when lightning strikes periodically...  If you enjoy the additional environmental annoyances they are yet another cool thing that makes NG2 the best of the bunch (though if you dislike the environmental stuff they aren't so challenging that they intrude on your enjoyment of the Ninja action.  

Graphics = 8

Ryu is a well-animated, cool-looking Ninja, and the way he jumps and does Ninja flips is pretty iconic.  He fights a wide array of evil-looking enemies, the boss characters are big and menacing.  The levels that Ryu runs through are very pretty, atmospheric and feature cool graphical effects such as scrolling backgrounds (the train level comes to mind).  Also, the graphical style of the game's cutscenes take a turn for the better, the people are presented in less of a graphic novel, more of a vaguely anime-inspired look, Ryu comes across as younger looking, people generally have more personality, or attitude, or demonic freakiness depending on the character... Ryu looks less like a middle-aged pair of angry eyes like in the first game.  Overall the graphical presentation is solid.  

Sound = 9

There are satisfying and appropriate sound effects in this game, but like many games of the NES era this game really amazes with its music.  if you don't touch the controller at the title screen and watch the opening movie, you can hear a really haunting melodic intro to the game which makes the evil Ashtar seem fittingly evil.  Also, many of the rousing tunes that go with the ninja action pull a Megaman and include an introductory riff that is not included in the track's infinite loop--there is an attention to detail and high-quality level that shines through in the game's musical stylings.  

Addictiveness = 8  Depth = 6

The high quality ninja action will keep gamer's glued to the screen till the credits roll.  The episodic nature of the levels and the inclusion of checkpoints are very helpful in keeping the frustration level down, you don't go back too far if you die, only if you run out of lives, but when you run out of lives you feel like you deserve to be sent a little farther backwards, so it's not too frustrating to get back to the latest challenging spot to overcome.  While it's addictive, the game comes from an era prior to easter eggs, unlockable achievements etc, and the only replay value to be found is when you replay a level after you die, the game pretty much gives you everything on its one and only go so you may not feel inclined to beat it again until the buzz of beating it the first time wears off.

Story = 10

NG2's cutscenes tell quite the interesting tale of evil cults bringing demons back to life, being stopped only be ninja dragons and his friends... the story is good and blotched with scary/dramatic/sad moments.  It's quite good!!

Difficulty = 9

Ninja Gaiden games are challenging... due to the slick play control, and Ryu's ninja abillity to stick to walls and things, the platforming itself would be super-easy if not for enemies coming from every direction to take the Ninja down.  The guy responsible for bringing Ninja Gaiden into the 3d world (starting on the xbox---btw ninja gaiden on the xbox is definitely one of the greatest action games ever) criticized the NES era games by saying that the challenge involves memorizing where the bad guys appear, and while I agree that memorizing where they show up can help with the particularly tricky spots, I paid attention to the experience of playing through the levels and I found that I did not have the enemy locations memorized, and even if I did that would not solve a lot of the problems that arise, the sort of thinking-on-your feet gameplay is more present than that dude gave it credit for, if there is an axe-chucking baddie, for example, knowing where he appears is less important than keeping sharp and getting in close between his thrown axes (or eliminate that risk and chuck a special attack at him)... anyways, the game is pretty difficult but in a fair sort of way, if an enemy does knock you to your death you probably made a bad judgment call in the final moments prior to death...

Overall, NG2 is highly recommended for people looking for Nes-era ninja action.  Keep those fire wheels spinning!

Nice review here. Plenty of detail, neatly written, categorized, and just nicely done. Keep it up.