We all expect CGI and special effects these days, but when a film does'nt rely on a ton of add on's to prop up an unfolding storyline you can often be pleasantly surprised.
Not fast paced by any means, but I was drawn in as the characters were believable given the rather unusual apocalyptic scenario.
No explanation as to how or why this scenario occurred, but how the characters handled/coped with the emotional aspect of their unanswerable situation was very thought provoking.