This is the first screen version of a John Steinbeck story. He adapted his novella into a play, which is what we see here. It isn't opened out to show the working farms of California which exploited the victims of the depression. This is an actors film, about the interaction between these rootless wanderers.
Mainly the famous protagonists. Lon Chaney Jr. is Lennie, the simple minded giant who unwittingly kills what he loves, or feels pity for. And Burgess Meredith is his benevolent keeper, George. Chaney's performance is unsubtle, but as a combination they are emotionally unstoppable, as is the pathos of Steinbeck's moral tale.
The rural poor are distorted by what they lack: a home, family, security. And self respect. They are in fear of a lonely, miserable old age and get by on the dream of a better life that will never happen and is as intangible as religious faith. Their (all male) community is as blighted as the survivors of a post apocalyptic wilderness.
This is far from the depression of Frank Capra. Lewis Milestone directs the limited space with fluency, but mainly conducts the excellent performances, with Betty Field a standout among the support. Aaron Copland's score brings shade to the visual austerity. It feels like group theatre but it's my pick as the best of Steinbeck on film.