Drakengard (the first of the series) was written in response to the flippant way many games are framed: You usually score higher the more enemies you kill. Yoko Taro thought that only an insane person would actually think that way.

So he created a game where the main character is literally broken and insane, killing huge swaths of enemies in a continually escalating apocalypse beyond his control. Throw in additional party members who are also broken and insane, and some point of view personalities commenting on how utterly horrible everything is, and on if the player is as insane as the character is.

It's not a great game and quite dated, but definitely has a message to explore which makes traversing the horrible contexts worth it. He went on to make Drakengard 3 and the related NieR games as well.