I really liked underlying premise of this movie, specifically that the millions of people killed by a cataclysmic event became ghosts, or remnants. In addition to this novel concept, the acting was good, and the characters' motivations and actions were logical and intelligent. In fact, I can't think of a single instance where extremely poor decision-making was used to advance the plot, setting this apart from most horror/thriller movies.
On the minus side, there were a number of plot holes and cheesy bits. Although they weren't bad enough to ruin the movie, there were enough of them that I can only give it a 7/10.
Overall, it was an enjoyable movie, and I would recommend it.