Loosen the movement controls. The player character feels like they're moving too fast, too quickly. The biggest thing that ruins Dynasty Warriors for me is the character movement, and Ni-Oh seems to have taken that from DW.
Move attack to R1, and overall use Dark Souls' controller scheme as a jump-off point. There's copying something to be identical, and then there's copying something because it works. Team Ninja needs to understand this. You can't properly manage your camera if you're busy managing attacks with that same thumb. Shooters know this, Dark Souls knows this, and Ni-Oh should know this.
Enemies hit too goddam hard. There's a difference between natural and artificial difficulty. Souls games are naturally difficult (until Ng+), but two hit kills from standard mobs feel like Koei is just artificially increasing the difficulty where, honestly, it isn't necessary (enemy AI is tight and dangerous, plus the penalty for running out of ki/stamina is brutal). Doing 25% less damage wouldn't compromise anything, while allowing at least one more mistake before death.
Overall, it feels like a wonderfully intimidating game. But that movement feels amateurish, and Koei needs to fix that (not just in Ni-Oh, but in ALL of their games).