The progress of the mission is slow, continuous and terrifying, but Kubrick never quite decided what he thought of the protagonist, Joker (Matthew Modine), and the perpetual half-smile on Joker’s face is an evasion that falls short of irony. Yet the strength of the movie comes from a different kind of refusal. Full Metal Jacket declines to say whether human nature is distorted by war or war itself is an emanation of human nature.
— David Bromwich (London Review of Books)