Okay I just played the demo and here's what I think:
1st things you'll notice, is ALOT OF DISMEMBERMENT. More so than the original games. I mean legs, arms, decappication out the wazoo. Ten times more blood than an average violent game should have that it's almost hiliarious! Serious overkills that make you say "Oh give me a break, that's too much now"
2nd, the New Ninpo Attacks are really awesome, however you must quickly choose your target and launch that attack before it wears out. LAME if you're in a hurry. Yet the results are some pretty fireworks and graphics of Earth, Fire, and Wind attacks
3rd, LAG in Ninja Gaiden? Ouch....I was facing alot of enemies and as soon as a large background appeared, the game seemed to lag alot.
4th, it's a tad easier than the previous NG games and I wasn't hardly damaged at all. Reminds me of the transistion between Ninja Gaiden 1 to 2 on NES (Same feel of gameplay, but 2 was alot easier compared to 1). However, it could be easy NOW, but that's usually not a good sign, because that tells me down the road, it's gonna get messy.
5th, a nice background cameo from DOA4 (You'll reconize the red bridge from Kasumi's stage)
6th, FAST gameplay, it's really faster than the previous game, so make sure to pay attention.
7th, the Button config is changed a little, but it's made more simplistic and more comfy to that of the 360's controller setup. I like it.
Honestly, I'm gonna say 80 out of a 100 on the grade scale, it's pretty good, but not amazing since it's the same ol' Ninja Gaiden we have all played and cussed at.