Ninja Gaiden Black challenges both eyes and mind: both have troubles believing what is happening.
The mind instead won't easily accept TeamNinja's choice of making a game so hard at difficulty level set to normal: boss battles are more often than not to be replayed several times in order to best them.
The game is unforgiving but not punishing. This means that - with the exception of the last but one chapter - you have a save point just before every difficult fight and that was a very wise decision on the developers' side.
Ninja Gaiden is at heart an arcade experience. And the technical level is simply impressive. Not only amazing visuals (excellent cinematics included) but also very good sound effects (while the music score is more of a mixed bag). The camera has been criticized heavily but it does the job most of the time. It can be irritating when you are hit from a foe you can't see but I like to think of it as an extra layer of challenge put up by TeamNinja, considering that it's not so unrealistic to have a limited view. The controls are sharp but it's frustrating to realize you can't control your character when it's in the middle of combos that last precious seconds, during which you have urgent need to access the inventory to heal yourself. This results often into an annoying death (especially against bosses that might deplete more than half of your energy with a single attack).
One fault of the game is actually a game concept fault (at least according to my vision): I would believe that some respawns are infinite. I can't be sure about it because once, I have been fighting an horde of enemies which I believed were respawning endlessly untill I instead was rewarded by a chest containing a very welcome item. After that, the enemies disappeared from the area. I can't say if this might apply also to other places where I believed enemies would never end respawning. If it's not clear, I simply hate respawning as game concept. It breaks the atmosphere and makes a game tedious and repetitive.
As for the "puzzles", they are the usual average ones: find a key of a certain shape to open a certain door, pull this lever to walk on the bridge and so on... Rather uninspired, albeit well implemented.
I did enjoy Ninja Gaiden Black and I can't but praise the developers for how marvellously they managed to squeeze every bit of power from the Xbox. This game requires that you as player are patient (and stubborn) enough to take a hard challenge. It is going to reward you immensely if you do, because it's often a rush of adrenaline and sheer joy.
As a small side note, from the intro (I played in japanese with english text: excellent voices) I am to believe that the sword my ninja is using is legendary. It's a bit cheapening its importance to have so many other melee weapons (I practically never used the original one) available. I would have rather had the player use his dragon sword (which is what you see him with in every cinematic piece) to be consistent with itself.
I recommend this game to anyone who likes action games. This game is just a couple of steps under "Prince of Persia: Sands of Time" (which is the absolute best action game I ever played) and it's a classic in his own right.