For me, NG3 is more tragic. Ninja Gaiden has a much longer legacy, and I feel like this is the first time where that legacy isn't being respected.
Ninja Gaiden 1 (NES) - Cinematics and an actual story in an action game. BRUTAL difficulty. Iconic enemies, power ups and hero introduction. This game is still relevant today and is still referenced by other games. A masterpiece.
Ninja Gaiden Arcade - I don't know if this came first, but it had a great beat-em up formula. Environment interaction being a unique feature.
Ninja Gaiden 2 - Definitive sequel. Improved upon the original's formula in every way. Ninja Ghosts that follow you and mimic your every move being the ground breaking feature. Another masterpiece.
Ninja Gaiden 3 - End of the trilogy. While it doesn't live up to the previous two games, it's still a competent action game in it's own right and tried some new things.
DOA - Keeping Ryu around in a fighting game. While not my favorite series, it did have some awesome features like the counter system.
Ninja Gaiden Xbox - A Modern classic. A reinvention of the series, but with plenty of homages to the original series (windmill shrunken, firewheel, etc.). Most brutal first level in the history of video games, IMO. IMO, it has the best enemies in video games, even today.
Hurricane Packs - I can't express how awesome a time it was during the Hurricane Pack introductions. You got to see the original developers going back to their code base and adding in a ridiculous amount of new features, enemies, levels, gamer interaction and balancing for free. I'd have to say this was one of my favorite eras in video games. Each time a new HP came out, we'd all go through the campaign again to see all of the changes and they were comprehensive.
Ninja Gaiden Black - A masterpiece. Nothing else needs to be said.
Ninja Gaiden Sigma - A lateral update. Some things are improved, but a lot of questionable design choices were implemented.
Ninja Gaiden 2 - Most ridiculous enemy interaction system I think I've ever experienced. Unbelievably well designed dismemberment system that served 2 goals. Giving players an extremely diverse, unique and interesting visual flair to the combat, while giving hardcore players an EXTREMELY deep gameplay system with many nuances. Still, this game is flawed in a number of ways, so it doesn't approach the mantel of NGB. If studio issues were not present, I believe that this would've been a masterpiece as well.
Ninja Gaiden Sigma 2 - Ugh. A LOT of simply incorrect design decisions, but there was a lot of new content developed. So, this one gets a pass.
Now, to NG3, I see nothing compelling. It's tragic. At least with DmC, there is some attempt being made to provide something new at least to the series. There is none of that with NG3, it's a complete regression.