Nioh is a new take on what is slowly becoming a new genre, one based on the formula set by the famous "Dark Souls" trilogy and its sibling, "Bloodborne". Both of which are excellent titles, and have spawned a number of similar games using a number of the same mechanics in the form of independant titles but Nioh is the first AAA attempt to my knowledge. The attempt has succeeded.
Nioh, unlike its inspirations, has an actual plot. That isn't a dig at those games, but they're more about a single goal surrounded by a mysterious world that you as the player must unravel. Here, you are playing an actual character by the name of William, an Irish sailor possessing a Gaelic spirit and who begins the game in a prison cell in the Tower of London.
Just wait, the Samurai parts start soon.
Unfortunately, you do have to play through what is the most bizarre first level I have ever seen. Mostly because it takes place before an actual tutorial containing the games primary mechanics even begins! Just know that the entire London stage is NOT, repeat, NOT indicative of what Nioh actually is and how it plays.
Anyway, your spirit gets stolen from you and you chase it to the land of "Zipangu", AKA Japan, which is currently embroiled in a massive war for the fate of the country. This historic backdrop is where you will actually play Nioh, whose primary mechanics involve the use of "combat stances", of which there are three (or four if you count "Sheathed Weapon", of which there are a handful of moves for) but you will primarily use three stances per weapon type. The combat is fast, faster than Bloodborne and much deadlier. If you aren't careful, you will die to as many as two-three hits from a large enemy of equivalent level.
Stamina management, or "Ki" as it is called here, is the means by which you will live or die. Opposingly, your opponents, even bosses, all have their own Ki meters. Ki can be "broken" by reducing either party's bar to zero through accumulated damage or over use of dodging or blocking. The game's combat also features an extensive tree of unlockable abilities based around each weapon along with two supporting trees of "Ninjutsu" and "Omnyo". Essentially spell casting. In a twist, you can regain stamina mid-combo or fight through properly timed Ki recovery techniques. A perfectly timed purification will often provide you with a damage bonus on your next attack, as well as purify any surrounding pools of Yokai energy.
Speaking of Yokai, when you aren't fighting human enemies you will for the majority of the game have to combat Yokai, or Demons, from Japanese folklore. The game's plot revolves around William becoming embroiled in the war taking place within the shadows of the larger one. Sort of like a, "secret history" thing. It takes him across Japan where along the way he will meet several historical characters as well as their spirits. Spirits who provide passive bonuses and a "living weapon" mode, which turns William's chosen weapons into elemental tools of destruction while providing him with limited invulnerability. The timer of which is reduced with damage or use.
As you can see there is a lot here and I'm having trouble keeping it all together. Basically what I'm saying is there is plenty familiar here but its all in a good way. The combat is slicker than From Software is capable of, however and I can't see how it can be argued. Team Ninja did a great job making that important aspect of gameplay stand out from its inspirations.
I'll end by answering the usual question, "Is it better than Dark Souls or Bloodborne?". Well, the combat certainly is. Bloodborne is close but the "Blood Gem" system is a mess that doesn't compare to Nioh's extensive upgrade and blacksmithing system. You can even play fashion Nioh and make your equipment look like other equipment you've found!
While the historical backdrop and the historical figures you meet along with the deep, Japanese mythology at play is a unique and fascinating backdrop it doesn't have the love, care and thoughtfulness of the Dark Souls and Bloodborne games. Not unexpected considering it is intentional, as all those games are designed to inspire thought and exploration in the players. World building in those games and how it is presented to the players is part of what makes them so good as From Software has mastered the abiity to tell a story without words, as it goes. Nioh is interesting but the story is just there to give you direction and purpose as opposed to the anmesiac wanderlust feeling of the other games.
From there, the other differences are minor enough because Team Ninja decided reinventing the wheel is pointless. The formulae works for the most part as is, so why mess with it? To all those who say, "Its just a rip off of Dark Souls!" I reply, "So you mean its more of what you already love?"