What are some of the ways in which Steinbeck makes the characters' reaction to the dream of living "off the fatta the lan'" so revealing?

The way the various characters react to George's dream (and it IS primarily George's dream; Lennie could not have created such a plan for himself) reveals their outlook on the world around them.  For example, Lennie envisions the little farm where he and George will live off the land as an idyllic Heaven, where everything is soft and no one will judge him for his (mis)behavior.  He sees his world as hard and harsh and...

The way the various characters react to George's dream (and it IS primarily George's dream; Lennie could not have created such a plan for himself) reveals their outlook on the world around them.  For example, Lennie envisions the little farm where he and George will live off the land as an idyllic Heaven, where everything is soft and no one will judge him for his (mis)behavior.  He sees his world as hard and harsh and constantly ready to berate him.  When Candy overhears George and Lennie discussing their plans, living off the land symbolizes escape and preservation for him.  After Slim gives permission for Carlson to shoot Candy's dog, he laments:

When they can me here I wisht somebody'd shoot me. But they won't do nothing like that. I won't have no place to go, an' I can't get no more jobs.

His attitude toward living off the land is one of last-ditch survival.  He agrees to contribute more than half the money for the farm and make a will leaving his portion to George and Lennie.  The farm represents one last chance for dignity for this old man.   For Crooks, the dream of living off the land is tempting . . . but only for a moment.  Although he does entertain the idea of being able to join the men in what would amount, for Crooks, to a return to slavery--he says he would work for no pay--he eventually recants his offer with this sad commentary:

They come, an’ they quit an’ go on; an’ every damn one of ‘em’s got a little piece of land in his head/ An’ never a God damn one of ‘em ever gets it. Just like heaven. Ever’body wants a little piece of lan’. I read plenty of books out here. Nobody never gets to heaven, and nobody gets no land. 

Each character has his own reasons for wanting to live "off the fatta the lan'."  These reasons give the reader further insight into the character and how he views the world.