George Segal gives one of his best performances as Lenny's friend and caretaker. The tenderness and love he puts across are subtle yet powerful and shows us the soul of a man who sees his relationship with his friend as one stemming from true affection and not mere obligation. It's a relationship that would be strained even among blood relatives, but Segal portrays George Milton as a man who still holds a dream for a better life even while coping with a brutal world on his own behalf and on behalf of his feeble minded childhood friend.
With very few bells and whistles, the design of a set can dramatically convey a mood. This film gives a telling example of how mood and theme can be conveyed through light, shade and texture.
Almost from the beginning we get the creepy feeling that something is not going to go well for George and Lenny from the somber tones of the world in which we find them. Visually, one can almost feel the despair of the Great Depression and its affect on the down-and-out who had to find some way to survive then, however meanly.
I recommend reading Steinbeck's humane masterpiece and viewing several other film adaptations of it to see the many levels at which this story can be told and interpreted.