You're right not to trust a film critic who calls a move stunning. But let me say this about Human Flow, the epic new documentary surveying the scope of the global refugee crisis, from the Chinese artist/activist Ai Weiwei: It stunned me, in the truest sense of the word. Again and again, over its 140 minutes, Human Flow overwhelms with its visions of populations in flight -- trekking down mountain roads with their possessions strapped to their backs; packed into open-air boats to cross the Mediterranean -- and then those populations stuck and stymied at borders, camping in ditches, sleeping under bridges, set up at expansive refugee camps in Germany and Kenya that seem to stretch on forever but of course are never enough.

Ai's technique here is to emphasize scale over specifics: More than 200 crew members shot this footage in more than 20 countries, often utilizing drones to capture the breadth of this mass migration. In this respect, Human Flow stuns: It reveals the full breadth of a catastrophe that we might usually think of piecemeal.

Ai's techniques establish a continuity of experience among divergent populations -- Syrians, Kenyans, Kurds, Palestinians, the Rohingya. We see the artist and director wandering the camps, chatting with survivors with his camera crew, often eliciting from a laugh from the people he meets. We meet no refugees at length and hear only scraps of their individual stories. The film, sometimes curiously beautiful, is above all else a challenge. Once you've seen the tent cities, the families living in filth, the children languishing bored and un-schooled in the wasteland between borders, how can you argue that fear or nationalism trump the human right to be?