Nue is the best boss in a non-FROM game, but every other boss is not very creative or interesting.

Nioh is without question one of the hardest games in the Souls genre

The story, atmosphere, etc isn't as good as Dark Souls, but it's still decent enough

Nioh is 90% co-opable (except for a few random missions for some reason), while Dark Souls is absolutely shit at co-op (except for a new mod that just came out)