It's because Nioh is so much more complex and evolved compared to everything else, that indeed they seem too different.
Most people play Nioh, finish the game and that's it, but the first run is basically a tutorial, the real game starts when the new difficulties are unlocked, each one giving more building options and requiring more and more of the player skills and that's the main difference... Mastering Nioh is a complete different thing to mastering any other souls games.
Nioh, like Ninja Gaiden, is quite complex, which unfortunately works against it, since most player's don't want to mastery a game.... And since the level design of Nioh is quite inferior compared to most other souls like games, the combat unfortunately isn't praised enough.
It's basically the same stuff that happend on DMC vs Ninja Gaiden vs God of War vs Bayonetta... They're all kinda the same type of game, is just that Ninja Gaiden is more complex (and in my opinion better because of that), while others have other good things that Ninja Gaiden lacks.
Anyway, a game made by Team Ninja and From Software, each working on their strengths, would be the best thing ever.
