This is going to be hard to answer, because it would require the person answering to have played both, and I know the likelihood of finding someone like thati s low unless they love the Hell out of Ninja Gaiden, like I do.

Now in Ninja Gaiden Black, enemies would be replaced by more difficult ones - from later on in the game - when you played on higher difficulties. Like on Normal, the first enemy you meet is a normal Brown Ninja. In Hard, a white Ninja Captain. In Very Hard, the dreaded Black Fire Ninja. In Master Ninja Mode, it was the Red Fire Ninja of all the horrible things.

More than that, though, once you got up to where the highest-tiered enemies were supposed to be, they would be replaced by new enemies altogether. Like those red dinosaur fiends? They'd be replaced by tremendous skull-wearing Ogre demons. I think those guys were originally in the Hurricane Pack. Shit, they replace a later boss with a much, much more horrible one. Then they start adding in bad-ass normal enemies to the boss fights! Things got well and truly crazy.

Does Ninja Gaiden Sigma retain these horrible but also awesome features? It may be relevant before too long.

I know one o' you folks has to know the answer to my simple, humble question!

Better place to ask is Iberian's NG forums.

Never played Sigma sadly... I do know that human head weighs 8 ounces though.

I have played Ninja Gaiden on the Xbox and Ninja Gaiden Sigma on the PS3. Although I haven't played through all the difficulties and didn't complete it either, I can confirm this:

1) Sigma has additional levels and weapons
2) Sigma is more forgiving.
3) I do not remember if the enemies are replaced by more difficult enemies, but I do know I found it easier to play through and as far as I can remember, you face less white ninja captains. In fact, playing Ninja Gaiden Sigma 2, I didn't even die once.

Not to say it's easy, because it's not, it's just more balanced.

If you are thinking of buying one, I would say in terms of content, you would be better off buying the Sigma version since they offer more, but if you prefere the insane difficulty then I would recommend you stick to the original xbox and 360 releases.

Also, in Sigma 2, the additional characters you can play with are awesome. They defo add a new style to the action. The characters vary quiet a bit e.g. there is a blond woman with this machine gun weapon and when playing with her you can attack from a safe distance and use gunfire combos.

I already own Black and NG2

Are you saying you never played Sigma on the higher difficulties?

I guess this can just be answered by anyone who played Sigma on higher difficulties