Check out Rotten Tomatoes for some great reviews of Children of Men. Here is the site’s overall view of the film:
Consensus: Children of Men works on every level: as a violent chase thriller, a fantastical cautionary tale, and a sophisticated human drama about societies struggling to live. This taut and thought-provoking tale may not have the showy special effects normally found in movies of this genre, but you won’t care one bit after the story kicks in, about a dystopic future where women can no longer conceive and hope lies within one woman who holds the key to humanity’s survival. It will have you riveted.