Ninja Gaiden isn't a ninja simulator; it's the best sidescrolling-to-3d-action conversion I've played in a looooong time. It would be like trying to compare Starfox (a 3D version of ye olde Gradius) with something like Wing Commander Privateer. They have the "space combat" in common, and it pretty much stops there. (I've loved both, and I'm doing WCP a grave injustice by putting it in the Tenchu side of this discussion)
As far as overall measurement in scoring goes; there is no comparison to the presentation, sound, controls and polish. Ninja Gaiden has shown what happens when a developer is given license to make the game they wanted to make, and not had to compromise. It's taking the DOA fighting engine (look at the combo presentations; it's given to you ingame) and applying it to a genre that generally has "A" for Attack, "B" for jump. The camera is VERY responsive; if it's at the wrong angle you can fix it with a button press. There is no sluggish or wildly obtuse procedure to look where you want to. It's too bad the camera didn't know which way you wanted to be looking automagically, but it's still great as-is.
I'll grant you this, NG doesn't provide the ninja experience that Tenchu does with all the sneaking and silent killing, but that wasn't it's aim. It was shooting for "ninja badass vs. the world".
Tenchu 3, IMHO, doesn't do the ninja experience justice either. It felt like a poorly repackaged Thief, or a shoddy mockup of Splinter Cell. Now, that's not to say I didn't like the Tenchu franchise; I *loved* Tenchu for the PS1. This one felt more like I was on rails. I didn't play very far in to it, mind you, as the "just another port" graphics pasted on a 51" widescreen TV was almost nauseating.
Let's have a peek, shall we?

VS.

Yeah, I was wondering... is her left hand holding the dagger behind the head of the guy against the wall behind her on the right side? Oh, and the texture for the brick wall would be a perfect addition to the Windows 3d maze screensaver.
So if you were hung up on sneaking around and killing people, check out any number of grade "A" games out there that let you do it. Splinter Cell 1 & 2, Thief DS, the upcoming Ghost, etc ...
If you love ninja games of all types, Ninja Gaiden is the better game, albiet less "realistic". If you need your ninja sim fix and you can't go without, go see Tenchu. Just make sure you're wearing beer-goggles. :wink:
And yes, those are biggest damned 2 pennies I could find.

[edited for grammar ]