I don't think anybody who has read "Of Mice and Men" has ever forgotten it. John Steinbeck paints characters who are so rich, so sympathetic, so tragic. I went through a brief Steinbeck phase during my highschool years, and every single novel – "The Grapes of Wrath," "The Pearl," "The Winter of Out Discontent," "The Red Pony" - left me feeling emotionally gutted. His conclusions are tragic and sorrowful, and yet somehow necessary - the only possible conclusion.
I've seen Gary Sinise's 1992 film adaptation of "Of Mice and Men," and it's a very strong, faithful adaptation, but this one tops it, I think. Snappy, shrewd George is played by Burgess Meredith, and he has a wonderful rapport with Lennie (Lon Chaney, Jr.), a behemoth with more heart than brains.
The characterisations are poignant, and the dialogue strongly literary, often lifted straight from the pages of the source material. Steinbeck has a delicate way of giving his characters hope, and then sharply yanking it away for the conclusion. This goes against every rule of Hollywood storytelling (even John Ford's 'The Grapes of Wrath (1940)' compromised with a more optimistic ending), but here director Lewis Milestone sticks to the original story like it was gospel.