I don't think that the length of the movie helped its development: as the stark minimalism surrounds us, maybe pointing out that we should concentrate on Nana and Nana only, I'd say it's fairly easy surrendering to boredom.
Fortunately, I've broken this barrier and got myself a decent enough twist.
There's a quality that goes beyond the execution itself. What is concrete? What belongs to one's own imagination? What becomes a part of the poetic depiction of one's mind? We won't know, but we can ask away... beyond the film, or should I say before it even turned into one, it is a dark silent tale told in an untouchable past and here we are, left to sense through a child's perception what became of that.
The answers we do not have, leaving us alone to our own thoughts, are this film's greatest asset.