Children of Men (IMDB 8.1|Rot 91%)
The human race is sterile and an 18 year old, the youngest person alive, is murdered. As this last child is killed, we see how the world has unraveled for the last 18 years. The world is in turmoil and anarchy, but "Britain Soldiers On" as a xenophobic police state. Children of Men looks at the struggle to live against this backdrop of despair and oppression.
Though thought-provoking, it is also has plenty of action, intrigue, and drama. It's filmed brilliantly. The camera unwaveringly shows us squalid refugee camps, torture, over-the-counter suicide pills, and terrorist bombings. Nonetheless, I feel the overall tale is one of hope and humanity. The absence of hope, humanity, children, etc magnifies how especially precious they are.
I am being purposely vague here, not because there are any particular twists in the plot, but because I think that the movie is best experienced with a fairly clean slate.
Go see Children of Men.