From what I read, the storytelling is awful, the gameplay is incredibly easy, and they took away anything that added depth to the series (like weapons and RPG aspects).
Mind you this is only from reviews though, I'm sure Hadrian can clarify.
Pretty much that and add a terrible camera that for some reason is a lot worse than the first game that came out in 2004. Unresponsive controls, at times you feel like you're not playing it at all!
It also has what I called "The Conduit syndrome" where you enter a room, you can't escape until you kill a wave of enemies (by wave I mean a party political broadcast) and then you do that AGAIN when you get to the next area. Its dull and repetitive, its not even fun for those who like that sort of thing because enemies are so easy to kill its ridiculous.
Bosses could have broken up The Conduit Syndrome had the bosses weren't repeated over and over, or even if there were different ways to kill the same bosses but sadly it seems like its a case of the developer just copying & pasting a previous boss.
I kept on playing it thinking "it'll get better, really it will" but it never did.
To be honest most of the reviews are spot on BUT I don't think the graphics are as bad as they make it out to be. Only played it on my friends 360 so I can't say if the Wii U/PS3 ones will look like crap or look better I can only go by what I've seen for myself.
To put it bluntly there is nothing here that Ninja Gaiden fans want, its severely watered down. I'd sort of understand if they wanted to find a new audience of some kind, I know some people are turned off by the difficulty but what they have changed isn't remotely good, the new ideas are awful and there just isn't anything that will attract new gamers to it.
Its a major fuck up for Team Ninja, its slightly better than Dead or Alive Paradise.