I like Ninja Gaiden a lot, but....yeah. It's overrated by the hack n slash community, not really the entire gaming community.
Difficulty is fine if its actually difficult, but being cheap is shit. NG2 is the worst offender. Thank God Sigma 2 fixed it.
The story is shit, the voiceacting is awful, the characters have as much personality as a pubic hair, the level designs are atrocious, and the animations are stiff as hell. I myself dont really like "canned" combos. Thats why I dislike Tekken. Remembering button press sequences is lame. The entire game is all about blocking and pulling out the same awkward looking combo ad nauseum.
I like a bit of customization.
That being said, Sigma 2 is a lot of fun if you play it like a normal person. I like mixing it up and shooting useless ninja stars and using crappy weapons and running around like a retard. Co-op is also fun.
Plus, titties. Lots of titties.