A. O. Scott in the New York Times:
There is plenty of sorrow to be found in “Into the Wild,” Sean Penn’s adaptation of the nonfiction bestseller by Jon Krakauer. The story begins with an unhappy family, proceeds through a series of encounters with the lonely and the lost, and ends in a senseless, premature death. But though the film’s structure may be tragic, its spirit is anything but. It is infused with an expansive, almost giddy sense of possibility, and it communicates a pure, unaffected delight in open spaces, fresh air and bright sunshine.
Some of this exuberance comes from Christopher Johnson McCandless, the young adventurer whose footloose life and gruesome fate were the subject of Mr. Krakauer’s book. As Mr. Penn understands him (and as he is portrayed, with unforced charm and brisk intelligence, by Emile Hirsch), Chris is at once a troubled, impulsive boy and a brave and dedicated spiritual pilgrim. He does not court danger but rather stumbles across it — thrillingly and then fatally — on the road to joy.
In letters to his friends, parts of which are scrawled across the screen in bright yellow capital letters, he revels in the simple beauty of the natural world. Adopting the pseudonym Alexander Supertramp, rejecting material possessions and human attachments, he proclaims himself an “aesthetic voyager.”