Either that, or you just like the same Devil Trigger launcher combo or aerial combo ad nauseum spread throughout the same five enemies and four boss fights, mixed up with tiny arbitrary missions and a terrible camera.
At the VERY least Otogi 2 has an identical level of depth, and where it lacks in a few combo finishers and weapons/tranformations it compensates with larger levels, more characters/enemies/bosses, and better overall variety. DMC is a shallow, dumb game whose only claim to fame is that some very specific combo timings and camera wackiness during the run-of-the-mill boss encounters tack on an exclusive level of difficulty. You like DMC because you're good at it, but that doesn't make it a top-notch genre entry.
Ninja Gaiden, on the other hand, *is* a significantly deeper game mechanically than Otogi 2 -- I won't deny that, but I like Otogi 2's weird over-the-top sense of style so much more.
That said, my initital comments are a bit disingenuous -- Otogi and Otogi 2 are more like Shinobi than any of the three games mentioned above.