Let me start by addressing the issues that many of the negative reviews here are highlighting. Most people are complaining about how this is a poor PC port because of performance issues. Perhaps they are right and it could be that this game requires mid-to-high end GPUs to run smoothly. I'm using a gtx 1070 and have only 2 issues with the game in terms of performance:
1) The mouse cursor appears in the middle of the screen when you start the game, or when you minimise and then return to the game. However, you can easily move your cursor to the top or bottom right corner of the screen to hide it. Yes, it reflects badly on the people who ported the game, but isn't a deal breaker
2) The cutscenes play at 30fps, and there's this weird translucent gray bar at the top and bottom of the screen during cut scenes, as though the game is trying to convert to widescreen format, but it just doesn't do so. Not sure if this is intentional or not.

Okay, on to the review of the game then. The premise of the game is that androids represent their human creators in a war against machines, who represent their alien creators, battling for control of the earth. You play as one of the androids.

Gameplay:
Nier Automata is an action RPG where the main combat mechanics revolve around hack and slash combined with shooter elements. In many other games, you can switch between melee and ranged weapons. But in Nier, you use your sword while at the same time controlling your pod (this small floating robot by your side) that fires bullets. You could rely on only shooting but then it'll take you a long time to kill enemies, and equally, you could rely only on your melee attacks, but enemies at a distance will be able to deal significant damage to you before you reach them. So this game is quite unique in that you have to use both your melee and ranged attacks simulataneously, and this can even be done on different targets at the same time.

The majority of the game is presented in typical 3d open world fashion, but there are areas of the game which switch the camera into a top-down or side-scrolling sequence. The transition is seamless without any loading, and feels very natural.

The RPG elements come in the form of a simple level up system. However, you can also upgrade your weapons, customise your plugins (which function as a substitute to active or passive skills in other RPGs) and customise your pod (the floating gun robot I mentioned earlier) to do other things apart from just shooting bullets or lasers. It's definitely not as complex other Squareenix games like Final Fantasy, but it's got a good level of depth as an RPG. If this sort of thing isn't your cup of tea, you could play the game on normal mode, or even easy mode, and basically, you can still win the game with minimal upgrades to your equipment or plugins.

Story:
Where do I even begin. If you've read anything about this game online, you'll probably have seen people waxing lyrical about how this game weaves a beautiful narrative about existentialism with various bits and bops of philosophy sprinkled on top, all while doing so in an engaging and approacable level. Everything you've read about this game is true. This isn't a game that tries to be deep for the sake of being deep. The creators of the game have a story they wanted to tell and they have done it masterfully here.

It's difficult to talk about the story without spoiling anything. There are a few plot twists that you will be able to see coming, but equally, there are moments well into the penultimate act of the game that will make your jaws drop. There will also be a lot of feels in the second half of the game. Basically, there's adventure, romance, mystery and tragedy all expertly interwoven in a well executed and epic narrative. If you've played any of the good final fantasy games, you'll at worst find this story as good as those in ff games, but more than likely you'll find it far better.

If you only play the main quests, it'll probably take about 20 hours to finish the game and unlock the final intended ending. But if you include the side quests, the game will take over 30 hours to finish. Some side quests were just boring fetch missions, but there are also some which add to the main story and lore. I myself skipped a lot of the sidequests, but I'm about to start a new save file now to complete everything properly.

Finally, what's great about the story are the many novel ways in which things are presented to the player. In most games, everything is done either by cutscene or by something another character tells the protagonist. Yes, there's plenty of that in this game too, but there are also the few moments of storytelling technique that can only be done via the medium of video games. I won't say too much on this to avoid spoiling things, but think Hideo Kojima/Metal Gear levels of stuff.

Music:
Every area in the game has a different soundtrack, and each one is beautiful. Every boss battle has its own battle theme and that just makes the fights even more epic. Usually, a game's music isn't worth talking about in a review, but believe me, this is something else.

TLDR:
Best game I've played in 2017 and even 2016 in terms of gameplay and storyline. Music is also out of this world. Bugs and performance issues should not affect high end systems. Buy it now and play it.