Long story short, very gimmicky and not worth it.
The food was subpar and extremely overpriced. The foods were very typical and boring, like... Grilled chicken, a Caesar salad, vanilla ice cream and chocolate cake, etc. The most exciting thing on the menu was perhaps the grilled octopus but it wasn't tasty, and I've had plenty of octopus before to compare and know how a properly prepared octopus should taste like.
The section of the restaurant that was lit didn't look too hygienic. Once inside the dark room, I was feeling the table and the chairs and some parts felt sticky.
The server was very friendly but service was incredibly slow. The only reason I'm giving it 2 stars instead of 1 is because the server was friendly.
We got a Groupon but taxes and tip were an additional $22. The food and experience were not worth it, even when the Groupon discount. The darkness didn't enhance the taste experience of these poorly prepared dishes.
I hear that there are better dark dining restaurants in other cities.