Probably really should've given this one star, but I gave it two for borrowing from Rod Serling's Twilight Zone. Can't remember the episode title, but it's the one where the earth is getting hotter and hotter, then it's twisted at the end to be really about the earth getting colder and colder. After Darkness, on one interpretation, does exactly the opposite. The sun rather suddenly goes out (I agree, this is not how I would imagine it would really happen), a super dysfunctional family struggles to survive, then at the last minute, the sun supposedly reignites, and all is well again, EXCEPT for that very last shot, where it kind of looks like maybe it's getting too hot, too bright, too fast. As in supernova? So, like any great horror flick, the monster isn't dead after all, it just takes on a new and terrifying form in the last few seconds, guaranteeing the 'heroes' will in fact all die, and all the personal growth they experienced is utterly wasted.
So, the philosophy of the film is totally bleak. Yes, the dad is a caricature and a narcissist but he's also 'right' about survival being important. He just sucks at being a leader who might actually help his family survive, because he lives in denial of the harsh reality of a sunless world. But the bleakness comes from the fact that it doesn't matter that he sucks, or that his black sheep son is really the strong one. It doesn't matter that the baby is born and all the 'nice' people can appreciate it but the dad keeps on being an operatic jerk. Because everyone dies anyway.
As for the heaven theory, I'm not buying it. I get the impression the mom is only telling the young daughter about heaven to make it easier for her to die. Logically, what sense would heaven make in a scenario where the whole planet dies? An event that final would contradict every religion I know of that has a heaven. So that's why I look at the ending as a classic horror flick double-cross, a supernova wipes them all out anyway, so even their brief moment of hope and renewed family unity and redemption is a complete illusion.
So, understood that way, the philosophy of this film is completely and cruelly nihilistic. I think nihilistic films in general are inherently disappointing for a lot of people, because human nature demands stories that teach us something useful about living life, i.e., surviving, and when we don't get that from a story, we tend not to like it.
And when you add to that the film's total reliance on disintegrating family dynamics, carried almost entirely by dialogue, with virtually no other plot infrastructure, this is why the film seems so boring to so many viewers. It isn't going anywhere, and it's taking the less interesting road to get there.
BTW, Melancholia was equally nihilistic, but the acting was stellar (pun somewhat intended), the ending was unambiguous, and there was never, to my mind, any false promise of redemption. It was all just, we humans are the only sentient life, and we got wiped out, and now the universe is completely void of meaning. After Darkness was an inferior telling of almost the same story.
As for the acting, directing, etc., I have seen worse. Much worse. The script was more likely the problem than the actors. It lacked organic flow. The writer wanted to paint these vignettes of the dysfunctional family, but the progression didn't feel natural, real. I kept falling out of the 'story immersion' and saying to myself, really?
Anyway, contrary to what many have said, I think you can find some value in it if you understand the premise is not really about science or action or even the apocalypse, but about how human weakness can lead each of us to our own individualized version of the apocalypse.
Review by jsbell from the Internet Movie Database.