I'm really disappointed. Based on the trailers I was interested, but in the end this game is just bad.
The gameplay is usal Dontnod game design. Neither good nor particularly bad.
But the narrative is the big disappointed.
The story is nothing.
The characters are nothing.
It's written worse than a mediocre CSI-episode.
And the eponymous "Twin Mirror" is just a advertising gimmick. It has no real impact on the story. To be honest it's quite irrelevant. No deep story about psyche or anything like that.
I love crime-thrillers and there aren't enough good crime thriller games. And Twin Mirror ist just another bad one.

The concept of the story is quite good. Promising material for an exciting thriller. But all in all it's poorly written. So many dialogues feel unnatural and artificial. Just like the characters and their relationships. The puzzles are "okay" I guess? But for me they feel half-heartedly integrated into the story.
The "gameplay" itself is really terrible. I am talking about the "story"-sections that are just wall of texts and more wall of texts. The presentation is a bankruptcy declaration to the art of visual story-telling. And don't tell me 'this is a visual novel. that's how this genre is made'. This is not an excuse for such weak presentation or writing. If that's the standard for this 'genre" than the genre itself is a bad (and probably cheap way) of developing games.
In addition if you don't play the game with a guide, you will probably have to play the same passages three or more times. This is just bad game-design.
So all in all I would like to see a movie or series adaption of 999, because the story is pretty decent. With a polished writing this could be really good movie / series. Uchikoshi himself said that he would like to make a movie or TV-drama adaptation of 999 together with JJ Abrams (I'm not sure about JJ^^).

Gameplay / Gamedesign: 2/10
Presentation / Artistic Vision: 3/10
Story / Writing: 6/10

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All in all 4/10