Jon Krakauer's bestseller has made McCandless a cult icon for a rootless generation - he graduated from college, changed his name, gave his money to charity, burned the rest, ditched his car (quite literally) and set off on an odyssey that ended with a survivalist challenge in a remote region of Alaska.
People tend to see some part of themselves in McCandless - a rebel, open-roader, wildman, back-to-the-garden greenie, activist, New Age Thoreau (he kept a florid journal). Certainly Krakauer did, noting how his own life as a solo mountain climber mirrored McCandless' dark side - brooding, aloof, impulsive to the point of being self-destructive.
In the movie, Penn gives us a substantially different view of McCandless - certainly it's a sunnier tale, and McCandless comes off as a guy who is more obviously inspirational.
Much of the difference in tone originates with Penn's decision to cast Emile Hirsh in the lead. Hirsch is an ingratiating young man with a naturally easy smile, and he makes McCandless a lighter, more optimistic presence that he was in the book.
The movie McCandless charms (sometimes heals) the people he meets - a wandering hippie couple (Catherine Keener, Brian Dierker), a rowdy grain harvester (Vince Vaughn), a lonely retiree (Hal Holbrook).
In return, almost everyone McCandless encounters offers him shelter, money, a job, a hot dog, sex, advice - something.
And this theme of hospitality and generosity helps "Into The Wild" take on a life independent of the book. It broadens from a portrait of McCandless to a landscape of back-road/off-road America, one that feels warm, authentic in its idiosyncracy and weirdly patriotic (it helps that Vaughn, Keener, Holbrook and Dierker are all good).