I managed to beat the second boss, who was a pretty generic take on the vampyric woman. Tough as nails at first, but once I'd learnt her patterns she wasn't particularly difficult.
I think part of the problem with Nioh's high opening difficulty is that the UI is a bit complicated and has more layers than a souls game. There's an upgrade tree for each weapon, and you'll want to make sure you get the upgrade which refunds you stamina after you dodge whilst said weapon is in hand. The other thing is that it is not uncommon for tough enemies to one-shot you, even if you have the heaviest armour set you can find equipped.
I'm not quite getting the hand-crafted sense you get from the soulsborne environments either, which is a shame. There are some nice little touches though, like returning lost spirits to the shrine and a few hidden areas. For the most part it's all pretty on-rails so far though.
I'm not sure I'll ever finish it because I can see myself lapsing from it before the end. I don't think it's bad, it's alright, but it requires a lot of concentration.