This is the game I love to hate.
What NG2 excels in is fast, fluid and brutal combat. You would be hard pressed to find a faster and more violent action game on the market. All weapons have a visceral feel to them and a long list of combos. In fact, the amount of combos that you can pull off sometimes makes it feel more like a fighting game. If the thought of memorizing combos makes you sick you can get buy on the easy and normal difficulties buy button mashing. Another strong suit of this game are the boss battles. Almost every boss battle is epic and will test your skills (some more than others, but more on that later). There is also a surprising amount of unlockables in the game (higher difficulties, costumes, gamer pics etc) which lends its self to replayability.
Unfortunately all is not well in Ninja Gaiden land. One major problem that was a constant annoyance was the camera. Most of the time the camera was unable to keep up with the action and made platforming element very frustrating. Another problem with the game was the inconsistent difficulty. For example, in one boss battle you must kill two giant dragons while at the same time having to deal with half a doze smaller flying demons. Then in the next boss fight you have to fight only one giant dragon with no support. Why does it go from hard to easy? That's one of the many mysteries of NG2. One another note, the story of NG2 is just plain awful (it basically boils down to bad guys are going to raise even badder guy, kill everything, girl with massive boobs).
In the end NG2 is a game you will love to hate. It will make you swear yell and cry (and possibly break a controller or two) but the gameplay is so satisfying that you can mostly look by these flaws.