What makes Steinbeck's style unique is his dual use of omniscient narration combined with a real empathy for his characters. Lennie and George are not educated and they are transients. But they also possess a dignified humanity.
Steinbeck also writes with lyrical beauty of the Salinas Valley, a beauty that always runs as an undercurrent, no matter how tragic or tortured the action of the novel.
Lastly, the "American Dream" is one the author extends to every man (and woman). Lennie and George hope for the same things everyone else does: a place to call their own and the continual pursuit of happiness. Although their dreams might be unrealistic, they are no more so than those of most people.