Nioh is a game about
Geralt of Rivia a British pirate who reads a book on a ship about the samurai, then dreams about how he'd be one and what weapons he uses and what guardian spirit he would inherit if he were a samurai. He then moves to Japan and embarks on an epic quest to be a true Japanese Samurai.
Also he mass murders a few thousand harmless spirits along the way.
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What is it gameplay wise?The fairest way to put it would be to say it's a Dark Souls clone. Its combat is more similar to Bloodborne but significantly less spammy due to the stringent stamina (ki) limits. Also instead of everything being Medieval / Gothic themed, it's based on Japanese folklore and the end of the Sengoku period.
It has all the staple Dark Souls mechanics. Bonfires (shrines), soul recovery (grave sites), punishing difficulty, player death locations (revenants), epic boss battles, enemies with good hitboxes and timing-based attacks, online co-op and online PVP, etc. etc.
What it has in addition is a ridiculously deep combat system that makes all the Souls games look childlike by comparison. We're talking gigantic movelists more similar to fighting games than an action adventure game. A billion skill trees, magic trees, ninja trees, clan trees, etc. etc. A ridiculous amount of loot along the lines of Diablo or Borderlands.
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What is it not?It's not open world like the Souls games. Rather, you have a hub map and areas in which you travel to for quests and subquests.
It's not bright. Souls games can be dark at times but you generally don't have difficulty seeing things unless it's explicitly designed for you not to see anything. Here, basically you will have trouble seeing most things.
It's not the prettiest game. Character models are alright but the texture work on some of the stuff is awful. Also the lack of lighting sucks. Though the bright levels are pretty good looking.
Easy. You're gonna die a lot.
A particularly amazing PC port. There's keyboard controls but no mouse support. And the FPS is very weird in weird locations. They have been releasing a steady stream of patches though. It's not a bad port by any means, but it's not great.
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Why should I play it?I'm not very good at explaining this but despite all the flaws I really, truly enjoy this game. So much so I pirated it, played for about 20 hours, then bought it, realized it refuses to transfer save files between legit and fake versions, then replayed the entire 20 hours again with a completely different build.
It's kinda like someone took the weapon systems and monsters from Monster Hunter and put them in a Souls game. So you have the deep and intricate loot + weapon mechanics from Monster Hunter, and the hardcore punishing combat from Souls. I think it's a beautiful fusion and that alone lets me look past all the flaws in the game.
I highly recommend it. The PC version is the complete version that comes with all the DLC and I can personally vouch that it has so much content you'll never play most of it. I have 34 hours in the legit Steam copy and I think I'm only halfway into the game. I am nowhere even close to starting the DLCs or the exalted NG+ or the supreme NG++. Yes, this is one of those games where people make a joke about how after you beat the game, you've only beaten the tutorial and the real game starts now.
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