I can agree with most of you here. It's true that the Ninja Gaiden series has been lacking on the story side... If anything, the next Ninja Gaiden should recapture Itagaki's vision of a ninja action game... heck, I'd choose Ninja Gaiden II over the NG1, Sigma 1 & 2, and definitely over Razor's Edge and the garbage version they called NG3. It's such an action pack game, keeping you on the edge of your seat, despite having all of your weapons upgraded and items at your finger tips available on your second play through of the game. It still manages to kick your butt regardless of how powerful your character has become with the new game plus. NG3 and NG3:RE on the other hand, well... the thing(s) that kept me and some of the fans from coming back for more, isn't just there. But I'm not going to criticize NG3 and NG3:RE here since everybody knows the story already.
As far as the story for the next Ninja Gaiden goes... I think it should start with a new series with a new protagonist. I really feel that Ryu's story has already been told and that Ryu should take a back seat and go for a really long vacation. I think Team Ninja should take notes of how Chris Nolan's Batman and Sam Mendes's James Bond have become so successful with their reboots. If Ninja Gaiden needs to tell a story, I think it needs to tell the story of how the Dragon Lineage came about. It has been said that the Dragon Sword has been passed down from generation to generation, so why not start there? Where did the Dragon Sword come from? It was said that it was carved out of a dragon's tooth... So how did that go? What's the story there? Personally, I'd like Team Ninja to tell the story of the origins of the Dragon Ninjas.
Gameplay-wise however, keep the same over the top-brutal action which made Ninja Gaiden II known for. Only top it off with different fatalities and different combos. More blood and more gore please!!!
Weapons: I'd like to see the new ninja, not only equipped with a staff, sword, claws, bow & arrow... but bring back the incendiary shurikens, tonfas, flails, while also introducing the sai and the kama weapons.
Upgrades: Bring back a Muramasa type shop. And for as long as I have enough credits/essence, I should be able to upgrade my weapons/health to maximum.
Magic: I want slots, not a meter styled magic. Team Ninja, see Ninja Gaiden I and Ninja Gaiden II and the Sigma series.
Health management/Essence: Bring it back to how Ninja Gaiden II utilized it... I'd like to be able to unleash ultimate techniques in an instant when there are essences around and especially when I have 15 or so enemies ganging up on me. I'd like to also be able to upgrade my health anytime I choose for as long as I have the life of the gods and have the talisman of rebirth at my disposal.
Enemies: No more virtual reality crap, alchemists, terrorists and especially a giant half-naked school girl (see final boss of Razor's Edge -- that's just plain sick man... am I the only one who thinks this way?). I want them to design enemies that looks menacing and can really pose a threat(s) to a dragon ninja... so keep the Spider Clan while also introducing a new ninja clan... perhaps the can be called the Cobra Ninja clan, Linkuei Ninja clan... I don't know, something unique. Bring back the werewolves and introduce the vampires, bezerkers, powerful demons and of course, the fiends.
Story: See above... it doesn't have to spend a lot of time showing cinematic scenes (MGS4 anyone?)... I just want a general story of the Dragon Lineage's origin and who are the fiends, really? And what is the source of the spider ninja's hatred towards the dragon ninja's? Where they once dragon ninjas themselves only to fall out of favor from the dragons, that they were banished from the dragon clan?... that's it! But please, I want wave after wave of enemies (see chapter 11 of Ninja Gaiden II).
Guest Protagonist(s): They are only welcome if they are allowed to be used for the entire single player experience. Meaning, perhaps, after beating the game with the main character the first time, unlock the guest characters and be able to use them other than the main character for the second play through. They shouldn't be inserted in the middle chapters because it breaks the flow of the game... and that's what I really hated with the Sigma series and Razor's Edge.
Character/Protagonist presentation: The whole point of wearing a mask as a ninja is to conceal their identity. The whole thing about Ryu removing his mask every time he cries is really annoying... The next ninja needs to shut up and only speaks with a few words. Don't humanize a super ninja that his number one job is to brutalize and butcher anyone or anything in his path... humanizing a cold-blooded killer (in a good way) don't go together... I'm sorry, but that's just my opinion.
Anyway, back to playing NGII.