Whats the difficulty like? I'm hearing its super hard.

Harder than Soulsborne.

The usual enemies are kind easy to defeat, but even if two of them gang up on it things get dangerous, a single 2 hit combo (which you won't be able to evade if you take the first hit anyway) from a standard axe wielding human can kill you at full life, at the beginning of the game.
The revenants, which are fallen players that you can summon, can also be pretty challenging.
The standard Yokais are also very dangerous, usually slow, but strong (there is exceptions).
And the bosses are pretty damn hard, some insanely hard (though I only fought 4 up until now, and 2 were on the demo).

I can't believe I saw some reviewrs saying it's not as hard as Dark Souls, those guys probably didn't play it at all, I kill most of the Soulsborne bosses at my first try, and the few bosses I faced on Nioh have to be fully pattern broke down to be beaten, though on Nioh you can have some great help while facing them, that's activating your guardian spirit, that makes you invencible while its active, so the fights can be exploited.

The overall difficulty of the game is high, but there is also a lot more into the combat than there is on Soulsborne, so fighting skill, not only evade and timing skill like on Soulsborne, are a big part of it, and being good helps a lot (being bad is also more of a trouble, lol).

It's around the same as Bloodborne, it starts hard but it didn't took me long to adapt, light armor for extra i-frames worked best for me, but it doesn't leave you much room for error.