That sounds awesome!
What HarkMahlberg means is that the game isn’t finished when you reach the credits.
When you replay the game a second time, you get the story from a complete different perspective. And when you start again after beating the game again, you get again a totally different experience from a different perspective.
It isn’t a spoiler though, it are basic game mechanics for Nier.
It is crucial to know you should keep playing after the credits. Because this isn’t normal for games. Otherwise people would get to the credits and think that’s the end.