(A full review in French is available here)
You'll spend a lot of time reading in this game, in fact there is almost nothing to do except reading the e-mails of the protagonist. The e-mail system is however well implemented, with the text appearing in real-time. Some might not like it (in fact I don't like when I cannot read at my own pace either), but it wasn't troublesome here because it really helped immersion.
And the game is immersive indeed. The state of mind of the protagonist is well retranscribed and you can feel her feelings. The game is well written too.
I found the end really amazing, though I cannot explain why without spoiling. If you like a game with a good atmosphere, you'll like this game. If you prefer "real" games, you should still give it a try, but you'll like it less.