The action doesn't let up. Be warned though, it's tough in more ways that one.
Setting and Story: Action games are not well known for their interesting stories or rich characters and Ninja Gaiden has forgone a compelling story in favor of refined action (not that I'm complaining). Characters don't have much substance to them other than "Bad-ass" in Ryu's case. And often, events often go unexplained. But anyway...
Ninja Gaiden stars Ryu Hayabusa (recognizable from the Dead or Alive series, although this takes place before those events) on a quest for revenge. After visiting his uncle Murai (and unexplainably killing all of Murai's ninja just to have a chat with him) Ryu returns to his village to find it burning and besieged by enemies led by an enormous Demon samurai. This creature (called a Fiend) is named Doku and has stolen the Dark Dragon Blade from Ryu's clan for his emperor. Defeated by Doku, Ryu sets of to Vigoor for vengeance, armed with the sister to the Dark Dragon, the Dragon Sword.
Ryu's search for the Dark Dragon takes him onto an airship and to Tairon, the capital of Vigoor. There, he is beset by it's military and monsters called fiends, humans that have been cursed by their blood and transformed by it. He meets a fiend hunter names Rachel and learn of the Greater Fiends, fiends that retain their souls and are very powerful. Doku being one of them. With the Dark Dragon in the hands of the Vigoor Emperor, Ryu fights through ancient ruins, military bases and the streets of Tairon towards the emperors palace...
The story won't win any awards, and the characters are pretty simple. Ryu has revenge on his mind and Rachel is searching for a particular fiend. It's really just a setup to the action. Gives it a reason to exist.
Graphics: Sharp and Shiny in all the right places. Team Ninja has done a great job making this game look great. And all without slowing down the game one bit. I've never encountered and frame-rate problems. The effects from the Ninpou (magic) are really nice to look at. As well as the weapon effects. One reason for the smooth graphics is that you never face more that 4 enemies at a time. Instead, new ones will teleport or spawn to replace lost ones.
Enemy design is good especially for bosses but most enemies come in at least 2 forms, meaning that you will see the same enemies in subsequent chapters although they are much tougher and usually have new moves.
I can't possibly forget the CG cut-sceens to this game. Some of the best work I've ever seen (even though they are all pre-rendered).
Sound: The music score to Ninja Gaiden is so good that you may opt to get the soundtrack (I did). There are some great standout tracks and some OK ones. They all fit the mood of wherever Ryu happens to be at the moment. The english voice acting is fine but you can't really tell since there isn't much talking done. Not much to listen to aside from battle noises.
Gameplay: The game is a little slow initially but gets a great deal faster after the first 3 chapter (out of 17). This is due to not being able to upgrade your weapon until chapter 2 and not even getting a second until chapter 4. Weapon wise, there are 6 melee weapons (plus one secret one) but I only really use 3 of them plus the secret one. 3 of the weapons are really just less useful version of other ones.
2 center pieces of combat are Ninpou and Unlimate Techniques. Your ninpou are simply Ninja Magic that ryu can unlease. There are only 4 but they are all very useful and 3 can even be upgraded with special items found in the world.
Ultimate techs are a staple of combat. When an enemy dies, it will leave "essence" floating in the air. Yellow essence can be used as money, blue gives health and red returns Ki (used for Ninpou). However, holding the Y button will allow Ryu to absorb these into his weapon (forgoing their other benefits) and allowing him to perform a UT. Each UT is different. Some do great damage to a single target but they all look really cool, do lots of damage and make you invulerable until you finish.
Replay: There are a total of 4 difficulties to frustrate you. (There is no Easy mode by the way). There is also the downloadable Hurricane packs for the master ninja tournament. It offers a new weapon and new enemies (and it's hard too). In addition, there are 50 golden scarabs hidden throughout the world. The reward for getting all of them is one of the original Ninja Gaiden games. Unfortunately, I don't think that it can be played if you are using an xbox 360.
Final thoughts:
+Action never slows except for one swimming section which no one likes.
+Great visuals
+Soundtrack sets the mood well
+Multiple weapons (both melee and ranged)
+Very memorable bosses
+I haven't found a single glitch yet.
-Story is not very compelling with many things left unexplained
-Often, you will fight through a dungeon and end up back at the beginning with no real sense of progression.
-The difficulty can be intimidation at times
-A certain enemy called the ghost fish, will drive you to new levels of undying rage.