A unique experience and certainly worth seeking out for a special occasion.
It does take a few minutes to get used to the atmosphere, but by the first course you stop trying to see things and just concentrate on the food, the chatter around you, and your companions. The tables around us seemed to be filled with loud, celebratory groups, but O.Noir is also a good choice for a romantic occasion, assuming your date is into it.
You would think they'd let the food slide, but no: It's first-rate and not gimmicky at all. We ordered from the menu before entering the dining room (there are "surprise" options for the more adventurous among us), and it was still a challenge to identify what was on our plates at any given time. This turned out to be tremendously entertaining, both because we really paid attention to each mouthful, and because sometimes we had to resort to eating with our hands.
(Don't worry, you won't be covered in food by the time you emerge. I was absolutely convinced we would embarrass ourselves, but we left looking none the worse for wear.)
The only issue was getting the attention of our server. He was absolutely wonderful: charming and soft-spoken. But there was a long period after dessert when we simply could not locate him. First, we called his name, then we chanted it, then we resorted to making up songs with his name in it. Nothing. After a while (How long? no idea.), he innocently turned up, asking how everything was.
This was not a big deal, but it made us realize that things can get strange at O.Noir. There is absolutely no way you can leave your table without the help of the waitstaff; don't even try it. So raise your voice if you need to. You won't be the only one.