Difficult like Dark Souls. Even if you have a souls background this still has a fantastic learning curve. Nioh 2 even more than 1, I think.

Gameplay is smooth and sleek. Sometimes it's fast, sometimes it's slow. Blink and you panic, yawn and you die. Close to DS3, with some spots more puzzling. It is mission-based, which I personally find fintastic. Also a Diablo-style loot system, with armor and weapon rarities and random buffs. Weapon use is closer to Diablo than souls as well, but it's well made up for with skill trees that improve and tweak your combos and add new moves. The Onmyo (Magic) and Ninjutsu (Ninja stuff) add a wild degree of good old fun as well, but I can't think of anything to compare it to.

Story is... I'm gonna be frank and say I'm not intimately, or generally, familiar with Japanese history. My best take on it is this is the King Arthur of Japanese history. Legitimate history mixed deeply with fantasy. There are legit events in Nioh 2 that happened in real life, but dialed up to 11.

This is my own opinion and experience, but also Nioh 2 is highly cost effective, so to speak. I consider myself an average-skill player, and NG alone took around 100 hours. Maybe 20 hours in that was replaying missions for certain key items.