If I had to sum up Nier in a single thought i would say that this is a Japanese or Japanification of the Zelda mechanic. It is odd to say that when Zelda is in and of itself Japanese, but this game essentially takes the Zelda mechanic and just loads it up with classic Japanese RPG tropes.
Nier on its surface is an adventure style brawler that follows the Zelda architecture of an over world connected by a multitude of dungeons. Through your game you collect abilities through the use of your magic book. The whole game though is just trivial nonsense filled with instances of sheer annoyance you will want to throw it across the room. The Zelda similarities stop pretty much on the surface and the whole rest of the game has a very distinct JRPG feel to it. The characters are set in that archetype, the inventory system, the leveling up, the grinding, the sidequests. All of it just feels so 1996.
Your main character plays as the father of a little girl. This main character though is so unlikeable and so unrealistically portrayed as a father you have absolutely no connection whatsoever to him. Partnered up with him is an unnecessarily fouled mouthed, scantily clad girl and a whit smacking book. The book, has some saving moments and good one liners, but the rest of the characters in the game are just so over the top and unlikeable there is no connection to them at all. In fact I dreaded every time the female lead Kaine opened her mouth. The language added nothing to the game.
You are set in an open world plain which has undeniable similarities to the plain in Ocarina of Time. And just like on OOT this world is devoid of pretty much anything. There are a few animals here and there and pretty much nothing else. Same goes for most of the dungeons and towns. In a world where Mass Effect 2 and Assassin's Creed exists, you simply cannot get by with these little places filled with 10 people walking their preset patterns. That hasn't been acceptable in nearly a decade in game design.
The battle mechanic of this game is very stripped down and is essentially a button masher. The problem is that there is no real combo system and it takes way to long to hack away at the enemies, even run of the mill ones, without it, so for even the simplest of fights you have spend time mashing at the "X" button with no visual flair for the player. It simply gets boring.
What perhaps annoys me most about this game though is the minor problems I see over and over in Japanese games these days that I cannot figure out why they are not fixed. Visually for example when you are in the town of "Facade" and travel on the sand barrage, the oarman's oar doesn't touch the sand!!!!!! That is just sloppy programming. Puzzles in this game are infuriating too. They are setup in such a way that again seem to fight with the controls. In one such dungeon puzzle I as the character am unable to run. Of course, mechanically your character almost immediately begins to run as soon as you hit the joystick.
The only saving grace for this game is the music. The score is wonderfully done and features some excellent japanese vocal tracks that add a great atmosphere. Had they been paired with a world that had some character in the slightest it would have made for great effect and mood. If the japanese designers do anything well it is over the top architecture and they could have excelled here are pairing some grand scenes up with this wonderful music, but it is just not there and everything falls apart.
Overall just avoid this one.