Sentence:  Once you find out what's going on—the girl is a “hungry,” this film's term for zombies—it's still interesting enough, if not quite as powerful. That's basically what you're in for with this British postapocalyptic survival horror tale, which starts off strong but dilutes its impact with every consecutive <WSD>reveal</WSD>. 
Meaning of the word marked with <WSD> tags:  A revelation; an uncovering of what was hidden.