I had the pleasure to see this movie some weeks ago at an exclusive preview in one of Germany's biggest movie theaters, Cinemaxx Essen. And I must say it really is a blockbuster altho its not a big budget production.
The movie's plot is your run-of-the-mill "And Then There Were None" (1945) story line: Put some strangers in a box and see who will survive; not particularly good, but not bad either. The dialogue and acting is amateurish, i.
I bought the DVD for this on Amazon, because I was so interested in the story and inside pictures of this former bunker. Luckily there is a making of describing most of the inside of the bunker.