First of all, Nier is a game developed by Cavia and published by Square Enix, but y'all know that. The version I played was the PS3 one, runned smoothly and while it had some frame drops in some parts, the whole game ran fluidly.
The story of Nier is...how to explain it without spoilers...just touching. Basically it's just a dad wanting to save his daughter, doing everything he can for it. But belive me, your perception of EVERYONE in the game will change in the NG+. It's somewhat post apocalyptic, but without guns or stuff. It's more of a rural post apocalyptic kind of thing. All the characters are really really well done, from Grimoire Weiss to Emil. The writing in the game is top notch, it's not your average JRPG writing. There's alot of parts in the game where the characters act real,
Voice Acting/Music: The voice acting is top notch. Liam O'Brien as Grimoire Weiss, Laura Bailey as Kainé, Jamieson Price as Nier and Jilie Ann Taylor as Emil, the "main" characters, make the whole voice acting really worthwhile. My favorite voice has to be Weiss one, his British-like accent and his sarcasm really match up together in a wonderful way. The music, I actually wished it had more tracks. The songs get repeated in the game, there are bout 40 songs. But every song is really wonderful. I got Kainé's theme stuck in my head for days, the ending theme really was something else, and the whole music really catched the "dramatic" feel in the game. I really liked every bit of music in this game, it was just awesome.
Graphics: Easily put: They suck. But the art style grows on you, and graphics don't really make a game. They could've been more polished, thought.
Gameplay/Level Design: The gameplay in Nier is your normal hack n slash action RPG. Well that's it until you get into some dungeons, then some ideas truly shine: Changing the game to a top view for a Diablo-like feel, making it a shump, a 2D platformer, it's all in here. Those parts really did something for what otherwise would've been a repetitive game in combat. The boss battles are truly awesome- some are of a really big scale and each one are pretty original. The magic sometimes made the game kinda more fun, and that's something I really appreciate. There's also the forest of myth/
Another problem is than it's pretty obvious the game had budget limitations. Even so, it's really enjoyable.
Tl;dr: the game is just great in story/voice acting/music, and pretty average/with great ideas in gameplay. I really enjoyed it. It was fun to play, the story really got you, and the whole game was just...great.